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brstevns
11-13-2014, 01:01 PM
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
11-13-2014, 01:43 PM
Did you slug your throat? If not, see LBT molds directions...

http://lbtmoulds.com/measurebore.shtml

Bent Ramrod
11-13-2014, 02:12 PM
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
11-13-2014, 10:04 PM
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
11-16-2014, 04:50 PM
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
11-16-2014, 06:07 PM
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
11-16-2014, 07:04 PM
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
11-16-2014, 08:21 PM
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
11-16-2014, 10:09 PM
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
11-17-2014, 09:58 AM
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
11-17-2014, 10:52 AM
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
11-17-2014, 11:00 AM
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
11-17-2014, 05:27 PM
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
11-18-2014, 09:49 AM
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
11-18-2014, 10:03 AM
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
11-18-2014, 10:49 AM
I am just bull headed. Really want this little RB to work with cast.

scottfire1957
11-18-2014, 11:59 AM
RB=rolling block, yes?

brstevns
11-18-2014, 12:20 PM
RB=rolling block, yes? That is correct!

DougGuy
11-18-2014, 12:30 PM
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
11-20-2014, 09:56 PM
I hope by counter boring the muzzle might be of help, as it is a few thousands larger then the bore.

MtGun44
11-21-2014, 01:45 AM
Interesting. My 7x57 Rem RB with VERY worn rifling will keep the LBT 150 gr at .285
diam inside of 2-2.5" at 50 yds with 18 gr of 2400. This is the only load that I have tried,
was skeptical that it would do anything even remotely useful, and quite surprised at
how well it did. All boolits hit straight, no leading, three groups, all roughly
similar, two had 4 of 5 in about 1.25" or so.

Plan on trying larger diam, but it hasn't bubbled to the top of the agenda yet.

Bill

brstevns
11-21-2014, 09:58 PM
Interesting. My 7x57 Rem RB with VERY worn rifling will keep the LBT 150 gr at .285
diam inside of 2-2.5" at 50 yds with 18 gr of 2400. This is the only load that I have tried,
was skeptical that it would do anything even remotely useful, and quite surprised at
how well it did. All boolits hit straight, no leading, three groups, all roughly
similar, two had 4 of 5 in about 1.25" or so.

Plan on trying larger diam, but it hasn't bubbled to the top of the agenda yet.

Bill

How is the muzzle on your rifle? Thinking this may be my problem.