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COAL and Jump to lands


Miseryguts

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Hi, I am in the depths of working up loads for a 308 win rifle, trying various bullets etc. Two of the bullets are of the tipped low drag variety (no names) when loaded to maximum SAAMI spec COAL (2.810) with this rifle have huge jumps to the lands (over 100 thou.) The "worst" has a jump of 127 thou when loaded to a COAL of 2.850, which just fits the magazine. 

Has any one else come across this, or is the chamber on my rifle out of kilter?

Not had chance to shoot these trial loads yet, as waiting for a gap in the rain!

M twiddling his thumbs and worrying in wet wet monmouthshire

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1 hour ago, Miseryguts said:

Hi, I am in the depths of working up loads for a 308 win rifle, trying various bullets etc. Two of the bullets are of the tipped low drag variety (no names) when loaded to maximum SAAMI spec COAL (2.810) with this rifle have huge jumps to the lands (over 100 thou.) The "worst" has a jump of 127 thou when loaded to a COAL of 2.850, which just fits the magazine. 

Has any one else come across this, or is the chamber on my rifle out of kilter?

Not had chance to shoot these trial loads yet, as waiting for a gap in the rain!

M twiddling his thumbs and worrying in wet wet monmouthshire

My rifle has a 100 thou jump with SMK155 when loaded to magazine length and it shoots well.  For sure it's better when loaded long but that may be other factors too.

Don't agonise over it. As JCS says;  just go and shoot it!

 

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Some bullets like a 5 thou jump, others 15 thou etc. Some even perform better jammed into the lands. 

If google Bryan Litz’s article on determinate best bullet jump for VLD bullets you will read that he advocates shooting two 3-shot group at jammed, just off the lands, 40, 80 and 120 thou jumps. There is no reason why you can’t try this with standard shaped bullets, so the only way you’ll find out if 100 thou is good or bad is to try it.

You didn’t say what weight your bullets are?

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I regularly shoot the SMK 155 (2156) and found, after a lot of experimentation, that in my rifle, with my load, .015" will give me a sub-0.5MOA group at 100yds.  Might not be right for yours of course.  Only testing will determine but that's half the fun. 

Very close to the Monmouthshire border....and also, very damp!!

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3 hours ago, Plecotus said:

I regularly shoot the SMK 155 (2156) and found, after a lot of experimentation, that in my rifle, with my load, .015" will give me a sub-0.5MOA group at 100yds.  Might not be right for yours of course.  Only testing will determine but that's half the fun. 

Very close to the Monmouthshire border....and also, very damp!!

Hi, yes, I load 2155(which I assume you mean in the above) to COAL of 2.800 to give a jump to lands of 45-50 thou, on top of 43gr N540 which last time out gave me 4 shot group 0.4moa at 200 yards - good enough for me anyway! The ELD(TMK) version of this (5155) is what is giving me the headache, as that bullet at COAL 2.850 gives a jump of 125 thou to land, and that means that the neck is only gripping about 0.25 inches of the bullet, nor will it fit the magazine and would have to be fed by hand. Not had chance to shoot these yet as we have gales and/or rain most days here - at least on the days I have time to go to the range as I have a shoot which takes up a fair bit of time also.

As I see you are near Chepstow, I assume you shoot at Severnside? Provided the weather is clement I will be there on Sunday to try these loads on the 200 yard range in the afternoon.

M

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ELD secant ogive bullets are reported to be very sensitive to load jump/jam.  I have found that to be the case too.  It's yet another complication for load development !

I shoot 155 Lapua Scenar and get excellent results out to 600yds.  The great thing about them is they are longer than SMK and still have good neck engagement when loaded long.

I've tried Hornedy ELD-M with very mixed results at .308 but with very good results with .338 out to 2000yds.

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On 11/1/2019 at 3:27 PM, Miseryguts said:

Hi, yes, I load 2155(which I assume you mean in the above) to COAL of 2.800 to give a jump to lands of 45-50 thou, on top of 43gr N540 which last time out gave me 4 shot group 0.4moa at 200 yards - good enough for me anyway! The ELD(TMK) version of this (5155) is what is giving me the headache, as that bullet at COAL 2.850 gives a jump of 125 thou to land, and that means that the neck is only gripping about 0.25 inches of the bullet, nor will it fit the magazine and would have to be fed by hand. Not had chance to shoot these yet as we have gales and/or rain most days here - at least on the days I have time to go to the range as I have a shoot which takes up a fair bit of time also.

As I see you are near Chepstow, I assume you shoot at Severnside? Provided the weather is clement I will be there on Sunday to try these loads on the 200 yard range in the afternoon.

M

Not 2155 - these: http://bulletin.accurateshooter.com/2008/12/sierra-introduces-new-308-155gr-palma-bullet/
 

I've never actually shot at Severnside although have been to Rogiet Moor, with Offas's Dyke RC quite a few times.  My home range is Monmouth.

I won't be shooting anywhere today though.  Did my back moving a bag of cement on Thursday and several hours of gutter cleaning and repair yesterday didn't help either.  Hope you have a good day.

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