Free bore effect on precision.

[Sgt. Brumbaugh]

I currently have a combination for my 338 LAI that shoots very well in my single shot action CTH, but will have too long of an AOL for a mag fed repeater I want to do. The reamer for the CTH has a .300 FB, I will need to reduce that to the .175-.225 range in order to keep the same jump to the lands as the current load and have it fit in the 4.050 MDT mag. I will have to reduce the base to tip loaded round from 4.1 to 3.9ish.

Bullet being used is a Berger 300 OTM

It is possible I will run into donut issues with a 3.9 OAL, but have inside neck reamed in the past and had no issues keeping great precision with a previous 338 LAI I had.

The bottom line is, if I do the new reamer- do I have a good chance that the same powder and jump will "likely" shoot well with the new reamer, or does a different FB length tend to change the powder choice / Jump, etc.

Current powder is N570.

 

[BoydAllen]

You can have your reamer reground. In either case I would send a dummy round. I like to have the option of touching the rifling. Just out of curiosity, how much are you jumping?

 

[Sgt. Brumbaugh]

You can have your reamer reground. In either case I would send a dummy round. I like to have the option of touching the rifling. Just out of curiosity, how much are you jumping?

.011-.012

 

[SKWERLZ]

Less case capacity will almost certainly
change your load.
.010-. 015 jump range seems to always shoot pretty decent with 300 OTM’s.

 

[jds holler]

I currently have a combination for my 338 LAI that shoots very well in my single shot action CTH, but will have too long of an AOL for a mag fed repeater I want to do. The reamer for the CTH has a .300 FB, I will need to reduce that to the .175-.225 range in order to keep the same jump to the lands as the current load and have it fit in the 4.050 MDT mag. I will have to reduce the base to tip loaded round from 4.1 to 3.9ish.

Bullet being used is a Berger 300 OTM

It is possible I will run into donut issues with a 3.9 OAL, but have inside neck reamed in the past and had no issues keeping great precision with a previous 338 LAI I had.

The bottom line is, if I do the new reamer- do I have a good chance that the same powder and jump will "likely" shoot well with the new reamer, or does a different FB length tend to change the powder choice / Jump, etc.

Current powder is N570.

You Sarge, are quite an acronymist! jd

 

[Sgt. Brumbaugh]

Less case capacity will almost certainly
change your load.
.010-. 015 jump range seems to always shoot pretty decent with 300 OTM’s.

I assumed that as well.