Advanced Marksmanship Chrono Differences for Gas vs Bolt Gun - ES / SD

[CPRifle]

My question is relatively simple, yet I don't expect a simple answer.

Can a gas gun (AR-10) introduce more variation in muzzle velocities for a given load than a bolt gun? I'm aware that gas guns often (and should) have lower average velocities. My question is with respect to variation in velocities, that is extreme spread (ES) and standard deviation (SD).

I'd be interested to see results from the same (low ES/SD) load fired through both platforms. Anyone have experience with this?

Thanks.

 

[treebasher]

Re: Chrono Differences for Gas vs Bolt Gun - ES / SD

My assumption is yes.

This summer while chronographing some 168gr FGMM in a Surgeon and a LWRC REPR I experienced a 10 fps standard deviation difference. The Surgeon had a 4 fps SD and the REPR had a 14 fps SD.

I'm not sure if I still have my notes, I think they went with the owner of the two rifles.

While the REPR is a piston gun I would suspect that you will see similar differences in a gas gun due to the gasses being vented off.

 

[SONIC SAAMI]

Re: Chrono Differences for Gas vs Bolt Gun - ES / SD

I have seen no ES/SD spread difference between a bolt/gas gun chambered in 6.5CM.
The bolt gun is aTac 30 action with a 24 inch barrel.
The gas gun is a DPMS with a 24 inch barrel.
Muzzle velocity difference between the two rifles is 40FPS.
ES of 15fps and SD of 5fps
This is for 10 shot strings passed over a Oehler

 

[BOLTRIPPER]

Re: Chrono Differences for Gas vs Bolt Gun - ES / SD

ohler is prolly THE gold standard.....

 

[SONIC SAAMI]

Re: Chrono Differences for Gas vs Bolt Gun - ES / SD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BOLTRIPPER</div><div class="ubbcode-body">ohler is prolly THE gold standard..... </div></div>

Yep...and a 10 shot string is a good base line

 

[CPRifle]

Re: Chrono Differences for Gas vs Bolt Gun - ES / SD

Thanks all, for the responses...

Kong, out of curiosity, do you use the same load in both guns? That is very similar to my current/future setup; tac30 26", and DPMS 24", but both in 260.

 

[SONIC SAAMI]

Re: Chrono Differences for Gas vs Bolt Gun - ES / SD

Yes same load was used in each rifle....41.5g of 4350 and a 140 A-Max bullet

 

[Swan]

Re: Chrono Differences for Gas vs Bolt Gun - ES / SD

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: "KONG"</div><div class="ubbcode-body">Yes same load was used in each rifle....43.5g of 4350 and a 140 A-Max bullet
</div></div>

I think you meant <span style="font-style: italic">41.5gr</span> of 4350... ?