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Re: .280AI Build

16 May 2019
@ 07:39 am (GMT)

Nathan Foster

Hi M.A, it helps if you have a false shoulder for the cases. If you have a .30 or .338 cal FL die with a tear drop shaped button, then it would be good to neck up, then neck back down again using another FL die. The cases should be a tight fit in the chamber with the false shoulder. This will help to prevent stretching at the case head.

After that, seat into the lands as you suggested. TB is fine, mild loads of 2213sc burn rate also fine (RE 22 etc).

1:9 is fine. The 3 contour finished at 26" can sometimes produce harmonic issues but is reflective of the steps taken to stress relieve the steel rather than whether it is cut or button rifled. But it may also be the reamer itself, issues at the throat. Or, the barrel may not have been lapped to finalize the dimensions.

The finicky performance you describe was discussed in the PDF I put together regarding the Foster Manson reamers.

I think that if you want a light weight build, it is worth taking some risks such as the 26" length. The barrel can always be docked later if it comes to it. But it does help to have a decent knox (see FMR thread). Other factors include a hand finished bore (regardless of the quality of todays CNC machining), an optimized reamer for modern bullets, sound bedding, concentric ammo (a major but generally ignored factor) and finally shooting technique.

Just as an aside, you might want to try testing this rifle with the ELD-X on the lands. You'll need to use a fire formed and partially neck sized case to do this, not an OAL gauge (see reloading book as to why). Obtain your max OAL and set your seating die up with the same projectile at the same max OAL. Record both the test projectile length and OAL length. Start with a mild load as the close seating will jack up pressures. If you are say .2mm off the lands now, then drop 1 grain. If you were 1mm off the lands then drop 2 grains.

When making up your ammo, you will need fairly good neck tension to ensure the projectiles do not get stuck in the chamber if you have to extract a case.

This might help alleviate some of the issues with your rifle.

If the throat is so long that you cannot get to the lands, then it may be best to quit soon. In these rifles, accuracy can be OK but as it falls away, you cannot chase the lands.

Also be aware that I am making assumptions here, guessing as to what might help you. I could be wrong about any and all points made here as I do not have the rifle in hand.


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