7mm-08 Case/trim length

[maltbuck]

Good evening, could do with a bit of help please.

Just started the reloading process for my 7mm-08, ( I have reloaded for a couple of years now for other calibres), and seem to have hit a head scratcher.

The trim to length suggested by Speer is 2.025, or Berger 2.0357.

Yet the once fired Norma cases (previous Norma factory loads) I have are 2.017-2.018, and once I have full sized them with a 2.5 thou knock back of the shoulders for headspacing, they are still only 2.020 - 2.021.

 

My thoughts are to use them anyway but trimmed to 2.020, but when I get either Norma or now Lapua new cases this will then affect my loads/accuracy, if these new cases are longer in the neck?? I recognise that these factory cases will grow with multiple firings / resizing but doubt they will grow by 5 thou on 2nd firing - it is never that simple!

 

I fully resize new brass anyway, so the actual headspace and hence case body dimensions should not be any different, it will just be an extra 5 thou in neck length? Or am I missing something?

 

And finally why are Norma factory cases so different to book length? Do they resize 308 brass?

 

Many thanks in advance.

 

MB

[jcampbellsmith]

I don't like trimming at all, so I would suggest going with a 2.025 inch trim length regardless of brand. Eventually the cases will get there. My Nosler 260 Rem cases started out < 2.020 and I won't trim them till they get to 2.027.

 

Anyway, I must go and trim some 6XC cases as I have only thirty rounds loaded at the minute and no prep'd brass.

 

Best regards

 

JCS

[The Gun Pimp]

Trim length is of course dependant on chamber length.

 

With a factory rifle/chamber there's usually plenty of allowance for the brass to grow but, if you have a custom rifle/barrel the growth limit could be minimal.

 

With my 6XC for example, I will trim brand-new cases otherwise, after first firing they will be very close to the limit.

[Laurie]

Berger is a bit out on its trim-to length it seems. Max SAAMI case-length is 2.035", and trim-too is normally 10 thou' less. As the Gun Pimp says, actual chamber length is something different again with large variations between factory and custom chambers. Even so, no chamber should be shorter than the SAAMI or CIP maximum.

 

Case-lengths as they come out of the box vary considerably by maker and lot, but again shouldn't exceed max SAAMI / CIP, although I've seen new unfired examples that strayed marginally over the line. Where shorter as in your case (no pun intended), it's not at all unusual with Norma which I've often found significantly under-length in several calibres with unprimed brass.

 

Your best bet is to trim them (with or without batching beforehand if there is a significant range of lengths) to a common value, then let them grow. Depending on your rifle's chamber and your loads, they'll soon grow as the 7-08 being based on the markedly tapered 308 Win shape can gain 3 to 5 thou' per sizing / firing cycle with heavyish loads. They never grow uniformly either just to be bloody awkward!

 

Some people are obsessed with having really tight uniformity and trim to the shortest length of the batch on each loading, but this gains the average shooter / rifle little or nothing. I hate trimming so much that I check everything in the box after sizing (important after not before especially if FL sizing) and only trim those that exceed SAAMI, or in some rifles those that are approaching the actual (measured) chamber length. So a box of 308s say for FTR will cover the full 10 thou' range from trim-to up to max SAAMI.

[maltbuck]

Thank you for your replies, particularly Laurie - I thought I was seriously getting something wrong when I was setting up the dies and measuring things!

 

Considering Norma is meant to be top quality and rivalling/if not surpassing Lapua brass quality, it seems a little odd that they are so short in case length against SAAMI standards.

 

King regards,

 

MB.

[Andrew]

Berger is a bit out on its trim-to length it seems. Max SAAMI case-length is 2.035", and trim-too is normally 10 thou' less. As the Gun Pimp says, actual chamber length is something different again with large variations between factory and custom chambers. Even so, no chamber should be shorter than the SAAMI or CIP maximum.

 

Case-lengths as they come out of the box vary considerably by maker and lot, but again shouldn't exceed max SAAMI / CIP, although I've seen new unfired examples that strayed marginally over the line. Where shorter as in your case (no pun intended), it's not at all unusual with Norma which I've often found significantly under-length in several calibres with unprimed brass.

 

Your best bet is to trim them (with or without batching beforehand if there is a significant range of lengths) to a common value, then let them grow. Depending on your rifle's chamber and your loads, they'll soon grow as the 7-08 being based on the markedly tapered 308 Win shape can gain 3 to 5 thou' per sizing / firing cycle with heavyish loads. They never grow uniformly either just to be bloody awkward!

 

Some people are obsessed with having really tight uniformity and trim to the shortest length of the batch on each loading, but this gains the average shooter / rifle little or nothing. I hate trimming so much that I check everything in the box after sizing (important after not before especially if FL sizing) and only trim those that exceed SAAMI, or in some rifles those that are approaching the actual (measured) chamber length. So a box of 308s say for FTR will cover the full 10 thou' range from trim-to up to max SAAMI.

I am one of those who trim to the shortest length of the bunch but I also crimp. Uniformity in length = uniformity in crimp.

 

As to the trim length of the 7-08: I reform mine from military brass and they all come out short; around 2.015". I use them anyhow with no problems.~Andrew

[Murph]

I am one of those who trim to the shortest length of the bunch but I also crimp. Uniformity in length = uniformity in crimp.

 

As to the trim length of the 7-08: I reform mine from military brass and they all come out short; around 2.015". I use them anyhow with no problems.~Andrew

Plus 1 on this. I trim with every fire as I also crimp. I find with any bullet that is loaded far from the lands. That about a 6 thou crimp will half my Extreme spreadand sd. I tried from the lightest crimp to a heavy crimp to see what the results were over the chrono. The lightest of crimps didn't do much till it got to the 6 thou mark. Anything over pushed the MV up a good bit and the extreme spread suffered. My bench is about 30 foot from my front door with my reloading shed beside it . I don't have to go to far to do a bit of testing. Lol

[Murph]

Forgot to say that this was with 223 brass. I have Altman trimmer with a sewing machine motor attached to it to speed up the operation. 2 free hands as I control it with a foot pedal. I quite enjoy trimming.

[Andrew]

Plus 1 on this. I trim with every fire as I also crimp. I find with any bullet that is loaded far from the lands. That about a 6 thou crimp will half my Extreme spreadand sd. I tried from the lightest crimp to a heavy crimp to see what the results were over the chrono. The lightest of crimps didn't do much till it got to the 6 thou mark. Anything over pushed the MV up a good bit and the extreme spread suffered. My bench is about 30 foot from my front door with my reloading shed beside it . I don't have to go to far to do a bit of testing. Lol

 

This has been my experience as well. I crimp all my loads using the Lee FCDs. If they don't make the one I want I have them make it custom. I have been wanting to try a tool marketed by a US company that is like a torque wrench that fits onto your press handle, allowing you to very precisely set the amount of crimp.

 

I recently chronographed my 308 loads built on Lake City surplus brass: They had an 11 fps SD over a 20 round sample. I'm certain crimping was a factor.~Andrew

[Murph]

This has been my experience as well. I crimp all my loads using the Lee FCDs. If they don't make the one I want I have them make it custom. I have been wanting to try a tool marketed by a US company that is like a torque wrench that fits onto your press handle, allowing you to very precisely set the amount of crimp.

 

I recently chronographed my 308 loads built on Lake City surplus brass: They had an 11 fps SD over a 20 round sample. I'm certain crimping was a factor.~Andrew

That's a very consistent load for sure!. When I got a really good load worked up without crimping, I decided to run 5 with a2thou crimp to see if the consistency got better. It got slightly better to be fair. But I decided to do batches of 5 with a 2 thou heavier crimp each time up to a 10 thou crimp. This is easily measured with a vernier caliper. I just put the calipers the crimped load about a a mill from the crimp. I reset the dials and then rocked the caliper gently till it dropped onto the crimp. This seemed to give accurate readings. From 2 thou to six thou the sd got better and better until it started dropping off to ten thou. Also the MV went up slightly and seemed to go out of the accuracy node aswell. My load is 130 thou off the lands and without the crimp my loads would surely suffer. 0.160 five shot group at 100 yards is my best to date. I only wish I could do it all the time. Lol

[Andrew]

Murph,

I have found that the amount of crimp necessary for optimal results depends on the brass and bullets to be loaded: the crimp that I put on my 308 is too heavy for my Hornet. That's why i wanted that torque wrench affair. I could catalog the crimp data with the general load data. I like your caliper method and will give it a try. I am currently just using a locking ring on the crimp die as a setting measure.

 

As an aside, I have been pondering jump to the lands. I have never been a proponent of seating a bullet "X" thou off of the lands in factory rifles with factory chambers. I have quite accurate loads seating to the data-specified OAL in all my rifles. (It's where I start my load development from) More fuel was added to the argument when i shot my Ruger 300AAC Blackout Friday evening with some Remington MATCH ammo. At 100M the ammo delivered clusters from a prone position. and earlier, my Nosler 125 grain handloads performed similarly. In both instances they were crimped, yes, but had a country mile to leap to get to the lands, I'm sure.

 

Maybe your loads wouldn't suffer as much as you think?~Andrew

[Murph]

Murph,

I have found that the amount of crimp necessary for optimal results depends on the brass and bullets to be loaded: the crimp that I put on my 308 is too heavy for my Hornet. That's why i wanted that torque wrench affair. I could catalog the crimp data with the general load data. I like your caliper method and will give it a try. I am currently just using a locking ring on the crimp die as a setting measure.

 

As an aside, I have been pondering jump to the lands. I have never been a proponent of seating a bullet "X" thou off of the lands in factory rifles with factory chambers. I have quite accurate loads seating to the data-specified OAL in all my rifles. (It's where I start my load development from) More fuel was added to the argument when i shot my Ruger 300AAC Blackout Friday evening with some Remington MATCH ammo. At 100M the ammo delivered clusters from a prone position. and earlier, my Nosler 125 grain handloads performed similarly. In both instances they were crimped, yes, but had a country mile to leap to get to the lands, I'm sure.

 

Maybe your loads wouldn't suffer as much as you think?~Andrew

I was thinking you would probably have variations dependant on calibers. I'd say you would get away with a heavier crimp on a larger diameter projectile. It would be nice to get a sweet spot for several different calibers and see if there's any correlation between crimp size and diameter of projectile as a percentage say. It sounds like an interesting experiment!. I found factory length loadings in my rifle were very accurate also. I always found when had a very good powder charge, messing around with the length did very little to shrink group sizes. My current load- 69 gr tmks with h335 is 100 thou over factory length 2.360 inch. The only reason it is longer is to stop compressing the powder. I'm not a big fan of compressing powder at all.

[Andrew]

I was thinking you would probably have variations dependant on calibers. I'd say you would get away with a heavier crimp on a larger diameter projectile. It would be nice to get a sweet spot for several different calibers and see if there's any correlation between crimp size and diameter of projectile as a percentage say. It sounds like an interesting experiment!. I found factory length loadings in my rifle were very accurate also. I always found when had a very good powder charge, messing around with the length did very little to shrink group sizes. My current load- 69 gr tmks with h335 is 100 thou over factory length 2.360 inch. The only reason it is longer is to stop compressing the powder. I'm not a big fan of compressing powder at all.

Yes. That would make and interesting experiment. Brass would need to be taken into heavy consideration. My Lake City 308 requires more than the Winchester I've used. Unfortunately, you, I and a few others (albeit, a growing number) share the belief that loading to specified OAL and crimping are a good thing. (tho oddly, most manufacturers fall into line with the practices) On another site I had one fellow absolutely refuse to acknowledge the two 20 round chrono data sheets I'd provided showing the reduction in ES and SD because he believed that loading to a certain distance off the lands was the ONLY "established" method to achieve accuracy. I explained to him that low ES and SD are not a guarantee of accuracy in a particular firearm, but more an assurance of consistency. That was the stick he beat me with for a while, not grasping that some rifles don't like some ammunition -even very good ammunition.

 

I'll look into finding one of those torque wrench affairs and see how they work. I think they advertise in "Handloader" magazine here in the US.~Andrew

[Murph]

Yes. That would make and interesting experiment. Brass would need to be taken into heavy consideration. My Lake City 308 requires more than the Winchester I've used. Unfortunately, you, I and a few others (albeit, a growing number) share the belief that loading to specified OAL and crimping are a good thing. (tho oddly, most manufacturers fall into line with the practices) On another site I had one fellow absolutely refuse to acknowledge the two 20 round chrono data sheets I'd provided showing the reduction in ES and SD because he believed that loading to a certain distance off the lands was the ONLY "established" method to achieve accuracy. I explained to him that low ES and SD are not a guarantee of accuracy in a particular firearm, but more an assurance of consistency. That was the stick he beat me with for a while, not grasping that some rifles don't like some ammunition -even very good ammunition.

 

I'll look into finding one of those torque wrench affairs and see how they work. I think they advertise in "Handloader" magazine here in the US.~Andrew

I too was one of those non believers!. My shooting buddy put me onto it about a year ago. I had no chronograph at the time so I had no way of checking. Try measuring with the calipers. It works really well. You can easily see a difference of a thou crimp with this method. I also use a locking nut to set the die also. When I am crimping I also crimp then turn the case slightly and recrimp to make sure the crimp collet overlaps also. With hornady 75 gr bthps I found no difference with crimped or non crimped rounds which was very strange indeed. Maybe it was the shape of the ogive or maybe they are harder copper and don't get as much of a crimp on them. I must look up that torque wrench you are talking about Andrew to see if it could bring something else to the table- you can never have enough gadgets!

[Andrew]

I too was one of those non believers!. My shooting buddy put me onto it about a year ago. I had no chronograph at the time so I had no way of checking. Try measuring with the calipers. It works really well. You can easily see a difference of a thou crimp with this method. I also use a locking nut to set the die also. When I am crimping I also crimp then turn the case slightly and recrimp to make sure the crimp collet overlaps also. With hornady 75 gr bthps I found no difference with crimped or non crimped rounds which was very strange indeed. Maybe it was the shape of the ogive or maybe they are harder copper and don't get as much of a crimp on them. I must look up that torque wrench you are talking about Andrew to see if it could bring something else to the table- you can never have enough gadgets!

I had a 30-06 in which the SD and ES didn't improve too much when I used H4831 over 165 grain bullets. Switching to 4350 and 4064 did show an improvement. At worst, it does no harm... and that is the common myth about crimping. Especially crimping bullets without a designated crimping groove. "Ruins accuracy!" Hasn't happened yet. My buddy is shooting his 6.5 Creedmore into less than 3/8" at 200 yards and he crimps all his loads using Sierra MK and Hornady A-Max. I crimp my 300AAC Blackout loads to very good effect. (Only mentioned because it's my newest project)

 

I will try your caliper method, with thanks in advance for the tip.

I don't rotate the case for a "full" crimp. It's already crimping such a huge percent of the total circumference that it never seemed necessary -to my way of thinking, at least.

 

If I can did up the ad in Handloader I will post it for you.~Andrew