Interesting ES/SD results on 2 identical rifles - 6.5PRC

[OzMike]

So I have done load dev on two rifles - 6.5PRC - Tikka Action, identical 24" Proof Research Barrels. Same stock. Same hour etc.. When fed the same load (hornady brass, eldx, AR2217) one of them has ES 29.6 and SD's of 7.4 the other has ES of 65.4 and SDs of 14.1 over 30 shots. Both shoot under 0.4MOA consistently.

Which makes me wonder when we talk about how the non-rifle factors that can be changed to improve velocity consistency such as neck tension, molycoating, brass, primer options, powder batches, bullets consistency etc.. whether it's all rubbish and it's just the luck of the draw or whether each rifle is unique and you don't need consistency you just need what the rifle likes?

Any ideas?

 

[R.Morehouse]

Yes....You got it......Find what the rifle likes, then be consistent with EVERYTHING else......Happy Easter

Regards
Rick

 

[6.5 forever]

So I have done load dev on two rifles - 6.5PRC - Tikka Action, identical 24" Proof Research Barrels. Same stock. Same hour etc.. When fed the same load (hornady brass, eldx, AR2217) one of them has ES 29.6 and SD's of 7.4 the other has ES of 65.4 and SDs of 14.1 over 30 shots. Both shoot under 0.4MOA consistently.

Which makes me wonder when we talk about how the non-rifle factors that can be changed to improve velocity consistency such as neck tension, molycoating, brass, primer options, powder batches, bullets consistency etc.. whether it's all rubbish and it's just the luck of the draw or whether each rifle is unique and you don't need consistency you just need what the rifle likes?

Any ideas?

You WILL need consistency if you shoot at longer ranges. You will NOT shoot .4 at 1000 yards with that spread. If your not shooting long range then your fine.

 

[drop_point]

Both shoot under 0.4MOA consistently.

Any ideas?

Then I'd say you're done and have nothing to worry about.

 

[Krogen]

Do both barrels have a similar round count?

 

[B Nettesheim]

Sounds like ignition inconsistencies between rifles

 

[Straightshooter1]

So I have done load dev on two rifles - 6.5PRC - Tikka Action, identical 24" Proof Research Barrels. Same stock. Same hour etc.. When fed the same load (hornady brass, eldx, AR2217) one of them has ES 29.6 and SD's of 7.4 the other has ES of 65.4 and SDs of 14.1 over 30 shots. Both shoot under 0.4MOA consistently.

Which makes me wonder when we talk about how the non-rifle factors that can be changed to improve velocity consistency such as neck tension, molycoating, brass, primer options, powder batches, bullets consistency etc.. whether it's all rubbish and it's just the luck of the draw or whether each rifle is unique and you don't need consistency you just need what the rifle likes?

Any ideas?

As "identical" as barrels might seem, there are differences (e.g. the same reamer will wear a little each time it's used causing some little difference in the next barrel it's used on). This is why many top professional shooter will buy barrels in batches and try them out to choose the one that shoots best. So yes, it has some luck of the draw. . . especially with high volume mass produced factory barrels.

 

[mgunderson]

What's the real question? SD of 14 and SD of 7 for a cartridge of that sizes is better than average. Were you expecting them to be identical? That is a very good area to be in. You are not likely losing matches at the reloading bench. Are these target SD or muzzle?

 

[Bill Norris]

Just another reason we know no two rifles are the same. Way too may variables go into each rifle from the ground up. As mentioned above reamers will cause differences even with barrels from the same stalk of steel.

 

[ebb]

Are the barrels carbon wrapped or stainless steel. I have often wondered if the carbon wrapped barrels had repeatable harmonics. Could this have anything to do with the differences in the way the 2 rifles shoot?

 

[drop_point]

Are the barrels carbon wrapped or stainless steel. I have often wondered if the carbon wrapped barrels had repeatable harmonics. Could this have anything to do with the differences in the way the 2 rifles shoot?

My carbon barrels are some of my most repeatable barrels. I’ve about got a 6.5 PRC toasted, and another in 6.5 Creedmoor is the most accurate barrel I’ve owned and over 20 rounds last time it had an ES of under 15 and SD under 6.

 

[OzMike]

Do both barrels have a similar round count?

one has 300 one has 200. Both have sped up already.

 

[OzMike]

What's the real question? SD of 14 and SD of 7 for a cartridge of that sizes is better than average. Were you expecting them to be identical? That is a very good area to be in. You are not likely losing matches at the reloading bench. Are these target SD or muzzle?

Sd was measured on a Xero at the muzzle. I was fine with it until I started shooting out to 1500y and realised that the ES on the bad barrel is enough to give me a vertical spread of 44 inches!

 

[mgunderson]

1500 complicates it more. If you are unable to tune out the vertical...... it is not a 1500 yard barrel. With that distance you will need to keep an open mind on possible influences.

 

[OzMike]

1500 complicates it more. If you are unable to tune out the vertical...... it is not a 1500 yard barrel. With that distance you will need to keep an open mind on possible influences.

I agree, the bit I'm not getting is that if my loads are consistent enough to give me good ES/SD on one barrel, why would I be getting double the spread on another identical barrel. I get 10% due to barrel variation but 100% increase makes no sense if it's all about consistent components (brass/neck tension/primers/weights etc..).

 

[Dos XX]

I'm not sure there is such thing as identical barrels.

Swap the barrels and see what happens.

 

[mgunderson]

Could be they are closer than the measurements indicate. Swap the barrels and shoot some through each barrel. I expect these are not lab measurements. Gun movement, chrono sample rates, pick up distances, ignition, wind, brass, bullet lots, barrel temps, ammo temp, barrel dwell time, chamber variations are all in play.

Are the average speeds identical? When I have barrel twins or triplets they are never the same speed.

My opinion is that you might be chasing a ghost. Your numbers are still very good. Shoot them and get better in the wind.

 

[FeMan]

I am not sure how big your sample size was in calculating the SDs, but the ES is typically about 3x the SD. Yours are closer to 5x and 6x. That implies to me that you may have a small number (one shot?) that is/are outliers.

You might want to check the fire control on the rifle with the high ES. Sear engagement, firing pin spring weight, fp spring clearance, fp protrusion, fp fall, etc can all affect combustion.