Muzzle Velocity Question...

Magoo22

Magoo22

CGN Regular
Rating - 0%
0   0   0
Location
Calgary
A friend and I are working up loads that have to be less than 2750 Ft/s

1 rifle is a PGW Coyote with a 1:10 twist at 24" the other rifle is an AI AX with 1:12 twist at 24"

Both barrels have about 2000 rounds and we are both shooting the same load components. Lapua brass with BR2 primers, Varget and Berger 175gr OTM TAC.

The Coyote is getting 2710 Ft/s with 43.1gr loads and the AX is getting 2680 Ft/s with 44.0gr loads. Speeds are from a Magneto V3 and shot at the same session so temp is likely not a factor.

CBTO in the Coyote is 2.2850 at 25 thou jump and CBTO on the AX is 2.2955 at 15 thou jump.

I understand that the deeper set bullet will have more pressure but it seems to me that there is more at play here. The difference seems extreme to me. The loads are consistent in both rifles as we are seeing ES's around 10 ft/s. One 1, 5 round group we saw an SD of 2.4 ft/s

Wondering if anyone can offer any ideas to help me understand why we are seeing what we are seeing. Is it possible that the throat and barrel on the AX are already shot out? Is there another explanation that eludes me?

Thanks in advance for your thoughts.
 
I can't speak for the AX, but here's what I'm getting with my Coyote:

178gr Hornady Match HPBT (pretty similar to SMK's)
CCI BR2 primers
Lapua brass
44.8gr of Varget
.010" off the lands
2830fps @15deg C (Magnetospeed v2 with ES=7 with a 10 round string letting the barrel cool between shots)

Just posting my results. And I don't think you have an issue. Oh, and my Coyote has 1057 rounds fired. And even with 1.7 more grains of powder, I think you can see the effect of seating the bullet longer.

The bigger question should be; how do they shoot?
 
Last edited:
They're different barrels. Different chambers, one might be smaller. Different freebore, lead angle. One barrel might have a smoother bore, or a tighter bore for that matter. One might be more heavily coppered then the other. There are dozens of variables that affect muzzle velocity.

One thing I can tell you is that the different twist rate makes statistically no difference in MV.
 
I would agree that 30 Ft/s is not that much difference. The thing that causes me to question it is that one is 30 ft/s faster with almost 1 gr less powder. If this is normal and there is that much potential difference in proper healthy barrels then that is great. That is what my question was about.

Also the question was asked about how they shoot and both rifles are easy at .5 MOA. We never questioned this in the past as the AI mostly shot 168's and the Coyote shot 178's. We looked for nodes that did not give pressure issues and generally sought the highest velocity we could. With the requirement to shoot 175gr at no more than 2750 these results came up and the question of why became relevant. One suggestion we got was that as a barrel starts to get shot out it loses velocity first and accuracy second.

No issue, then I will add this to the things that I understand and carry on. I guess 1 gr of powder is not that much when compared to 44 but when you spend time dialling in at less than 5% of that difference it seems bigger...

Thanks for the feedback folks.
 
Yes, the speed limit is for the limited division of the Riflemans Team Challenge. Going to give that a try this year. Similar to PRS but you shoot as a team with one shooter and one spotter. Hopefully less about doing yoga while shooting and more about figuring out solutions to make the shot. Will know more in a couple of weeks...
 
You must log in or register to reply here.
Back
Top Bottom