Berger 85.5 bullets

[Gater]

I have some loads for the .223 85.5 grain Hybrids but the loads I was given by Berger where fired from a 30 in barrel with a 1-6 twist I have a 28 in 1-7.7 twist anyone have any idea about how
FPS can I expect to loose

 

[LVLAaron]

30-40fps?

 

[Laurie]

Not very much, likely around 30 fps, maybe less. Different chamber freebores and barrel internal dimensions can make as big a difference. The difference in twist rate won't affect the allowable maximum charge weight or MV.

 

[dcali]

The variation from barrel to barrel is probably as big as the difference between 28” and 30”. 20fps per inch is a *rough* way to estimate when barrel lengths aren’t dramatically different.

 

[dstoenner]

Not to mention that the 28 and 30 inch barrels might tune to different velocities throwing off any loss in velocity for a shorter barrel.

This is a system question with no way to really know

David

 

[Brians356]

The variation from barrel to barrel is probably as big as the difference between 28” and 30”. 20fps per inch is a *rough* way to estimate when barrel lengths aren’t dramatically different.

A couple of barrel chop tests I've read suggested 25 - 30 fps per inch as I recall. One was for 308 Win.
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[Ned Ludd]

According to Quickload estimates I made for the 85.5s with H4895 and a 30" barreled rifle set up to shoot 90 VLDs, the 85.5s were predicted to tune in a bit faster than the 90s (for which a good accuracy node falls around ~2850 fps) at a velocity range of 2870-2880 fps. It may be that with a 28" barrel and the lighter bullet, a tuned load will not give up any velocity at all. However, without having a calibrated QL file with the 85.5s/H4895 to make predictions, I would not rely on it to provide any definitive answers. If there is any decrease at all in velocity with the 85.5 for a 28" versus 30" barrel, I would expect it to be of little concern (i.e. less than 20-30 fps total).

For me, the bigger question might be how the pressure looks. Although it's certainly possible to reach the equivalent of the 30" barrel 2840-2850 fps node with 90 VLDs/H4895 in a 28" barrel, it takes more pressure to do it. Brass life for such a load in a 30" barrel is already very poor, and a shorter barrel would only exacerbate the issue. But again, we may be talking about very small differences that with lighter 85.5 gr bullet don't actually amount to anything worthy of concern. I'd let the rifle tell me where it wants to shoot, and where that falls in terms of brass life should be obvious once the load has been worked up.

 

[fatelvis]

I’m holding out until Berger comes out with their 85.75 bullet.