Bullet sizing Question.

[brstevns]

Have a old Rem. RB in 7mm that is giving me fits. The bore slugged out to .288 and is in fair condition. I have tried sizing bullets from .287 to .293 and still key holes at 25 yards. I can put a .297 size bullet into the neck of fired brass. Should I size to .297? Was using a Lyman 287405. going to go to a Lyman .287308

[Yodogsandman]

Did you slug your throat? If not, see LBT molds directions...

http://lbtmoulds.com/measurebore.shtml

[Bent Ramrod]

Also slug the muzzle to a quarter inch or so in and compare that to the slug run through the bore. A trumpet shaped muzzle is a guaranteed keyhole generator.

This condition can be very hard to spot by eyeball only; the rifling can look as good as the rest of the barrel.

[brstevns]

Also slug the muzzle to a quarter inch or so in and compare that to the slug run through the bore. A trumpet shaped muzzle is a guaranteed keyhole generator.

This condition can be very hard to spot by eyeball only; the rifling can look as good as the rest of the barrel.

That may well be the problem. I need to check this out. I guess 1/2 inch or so would need to be removed if this is the case or counter bore the muzzle?

[David Caldwell]

What's your load? !500-1600 fps with a gascheck sized around .290 should work. If no gascheck start around 1000 fps, increase until they tumble or accuracy fails to meet standards then back off.

[brstevns]

What's your load? !500-1600 fps with a gascheck sized around .290 should work. If no gascheck start around 1000 fps, increase until they tumble or accuracy fails to meet standards then back off.

Load is around 1440-1500 FPS been using gas check but still getting key holes. May will be a worn muzzle, think of counter boring to see what happens.

[MarkP]

I have a 7 mm RB; while shooting groups I have had some hit the target sideways at 75 yds. My bore is in fair condition, my chamber near the should neck junction has a slight bulge or like a step in the neck. When I reload I keep the step in place and index the cartridges by head stamp when inserting into chamber.

[brstevns]

I have a 7 mm RB; while shooting groups I have had some hit the target sideways at 75 yds. My bore is in fair condition, my chamber near the should neck junction has a slight bulge or like a step in the neck. When I reload I keep the step in place and index the cartridges by head stamp when inserting into chamber.

Chamber seems to be alright but for the large throat area. Looking for a better barrel to put on it.

[Echo]

Are the boolits being swaged down on seating? What is the diameter of the sized & expanded case? What alloy are you using? Are you using a Lyman M die? What is the neck wall thickness? What is the OD of the neck w/boolit seated?
I believe this is the problem...

[44man]

Keyholes are almost always a mismatch to twist. Spinning a boolit too slow is the cause.
It has been written that boolit length is used to determine twist but I believe it is drive length of the boolit that counts. You might be way too slow.
Dump shot gun powders, get a slow powder and work up.
You said 7mm but what 7mm? What are you loading for powder.
That boolit has an extremely long drive length, I bet 1900 to over 2000 fps is needed.

[brstevns]

Keyholes are almost always a mismatch to twist. Spinning a boolit too slow is the cause.
It has been written that boolit length is used to determine twist but I believe it is drive length of the boolit that counts. You might be way too slow.
Dump shot gun powders, get a slow powder and work up.
You said 7mm but what 7mm? What are you loading for powder.
That boolit has an extremely long drive length, I bet 1900 to over 2000 fps is needed.

The RB is a 7mm or 7x57 as know today. Most of the time the shoulder on the RB is just a little different then the 7x57 round. Was using Unqiue but have also used IMR 4227. Thinking of trying IMR 4198 around 20gr load with the Lyman 287308 that is a 165gr bullet with a gas check.

[leadman]

Add a filler of poly-fil as this has helped my loads in marginal bores before. A grain or less should do.
The chambers of the RBs are longer than the SAAMI 7 X 57 we know today so fireforming and neck sizing helps.

[brstevns]

Yes I have been fireforming and neck sizing. Only been sizing enough of the neck to hold the bullet. Will give the filler a try.

[44man]

Might try 3031 or 4895 too. The 7x57 is a great caliber but I am not familiar with the model gun.
I was having fits with my Marlin 30-30 until I went to those powders, tried all the fast powder loads and 4198, seems a very touchy powder.
Varget might work wonderful too.

[white eagle]

alloy may be another issue
I gave up on my 284 bore because of the same issues you were having
recently switched to more cast friendly cals. (30-35-44-45)

[brstevns]

I am just bull headed. Really want this little RB to work with cast.

[scottfire1957]

RB=rolling block, yes?

[brstevns]

RB=rolling block, yes?

That is correct!

[DougGuy]

Yep, there is too much unknown about your throat and bore to say specifically do -this- to it. 4895 rocks in my .308 it is the only powder I use for that caliber. 3 into a guitar pick @200yds is the norm.

[brstevns]

I hope by counter boring the muzzle might be of help, as it is a few thousands larger then the bore.