How Long Is To Long?

[jay666d]

A while ago now, when I first decided to start home loading, I crudely measured for my bullet length.

 

I developed a load based on this and had good results.

 

When I had my rifle re-barrelled , I used the same crude method again and developed a load for 80Gr Amax's. Right off the bat, I had amazing results.

 

When using my bullet seater, I was forever getting variable measurements in the overall length... No doubt down to varying size bullet tips.

 

So I decided to upgrade some of my equipment... Competition Bullet Seater with an A-Max spesific stem. I also got a comparator to measure from the Ogive, and a Hornady OAL Guage to properly measure for bullet length.

 

Using the new measuring tools, I have discovered that I've been 'Jamming' the bullet almost 70 thou into the Lands! I couldn't believe it.

 

I decided to back off my Lands a little, 20 thou... This sent the bullets sideways thru the target. ( Ones that made it to the target anyway!)

 

Jamming them 20 thou helped straighten them up again, but I've not tried any groups with them yet.

 

So I know that jamming them 70 thou gets the results I'm looking for, and I was shooting like that for a long time completely unaware that they were so far into the Lands... Is it to long?

[terryh]

Jay,

 

There are folks here that utilise toching/jaming into the lands extensivly so can comment more, but 070 sounds a lot, almost 2mm.

 

My first thought would be are your bullets actually .070" into the lands - could the bullet be being pushed back upon chambering?

 

Have you ever removed a chambered round and measured it again (by pushing the round out using a cleaning rod NB take the bolt out first )

 

Just a thought?

 

T

[jay666d]

I thought it seemed a huge amount too!

 

I have tried it the way you suggest, and I keep coming up with the same answer! :-/

[jcampbellsmith]

It sounds a lot and I would be surprised you haven't at least noticed engraving marks on the bullets of rounds that you have loaded. One thought is to check the length of your OAL case versus your own cases. I take it we are talking about ,223 here?

 

The other thing to consider is that your A-Max have changed from one batch to another. I've seen 25 thou differences in Hornady bullet profiles from one batch to the next.

 

One question would be with respect to effort to close the bolt. For interest prepare a dummy round with the bullet seated 50 thou off the lands and see what effort you require to close the bolt.

 

Ultimately you are the man on the spot and if it shoots and you are happy, continue as is.

 

Regards

 

JCS

[1967spud]

with out a herrendous ammount of neck tension im guessing they would be a struggle to actual;ly seat that deep

 

have you pulled a bullet after chambering it and remeasured it?

[John MH]

Try inking a bullet with a black marker and then chamber it and then unload. The inked bullet should show where it is making contact with the lands, if there are no marks on the inked area it may no be touching.

[Chris-NZ]

An off-the-shelf dummy case for your OAL gauge may not be an accurate fit in your chamber and therefore under-estimating the base-to-throat length. The only way round that is to make a modified case from a fired case that came out of your gun

[jay666d]

All good points guys.

 

I'll check and double check my measurements, and I'll give inking one of the bullets a go too!

 

Yes, this is .223 and there all from the same batch. My original measurement, before I was measuring to the ogive was base to bullet tip, 2.550"

 

I can honestly say, when I was chambering my rounds they never felt difficult to load, and I never had one come apart when unloading a live round from the chamber.

 

:-/

[jay666d]

with out a herrendous ammount of neck tension im guessing they would be a struggle to actual;ly seat that deep

 

have you pulled a bullet after chambering it and remeasured it?

I did, and it remained the same size.

 

A quick edit on this answer...

 

I've just loaded another one, it seemed ok to push in, was a little stiff coming out and it pushed the bullet back .005"

 

Looking at the bullet, I can see clearly the marks left on it by the Lands.

 

Using the OAL Guage, it reckons my CBTO should be 1.935

 

Although I've had great results, I don't feel comfortable now I know they are so long and that they change size when I chamber them... I'll start with a 20 thou jam and go from there!

[Dr.T.]

Hi Jay,

 

If the bullet gets pushed back .005 when seated .070 into the lands, then I'd bet that it also gets pushed back when jammed .020 (although perhaps less - it'll be interesting). Ultimately, so long as they're pushed back by about the same amount (through consistent neck tension), then I wouldn't worry. And even if they're not, it gets a bit academic when they're already producing great results...

 

My main concern for a field rifle would be whether there's enough neck tension to keep the head in the case after extraction. Apparently there is, so I don't see much benefit in "fine-tuning" the jam. .020 is a reasonably hard jam anyway, so any extraction problems would likely exist at around .020 also.

 

Best of luck!

[jay666d]

I loaded rounds up with a 70, 60, 50, 40, 30, 20 and 10 thou jam.

 

10 thou was the only set that didn't get bumped back at all.

 

I loaded 50 rounds and got the results on the target that I was happy with. Over those 50 the SD was 11.8... I was aiming for under 10. (I shot them in groups of 5, some of the group SD's were coming out at 6-9 but another group closer to 18 let the average down!)

 

Thanks again for all the input guys!