Shoulder bumping question

Screwtop.243 · Aug 29, 2018

Hi guys,

I've been watching alot of the videos on Youtube over the past couple years by Panhandle precision. He advocates decapping as a separate step and controlling shoulder bump, recommending a .001 bump. I got the Sinclair comparator body and inserts and tried this with my 6.5-284 the other day. I bumped it .001 and still found it hard to cam the bolt on my Savage on a resized case. I found that I had to bump the shoulder about .005 to get what I felt to be a comfortable "camming" force on the bolt. Is this a function of a chamber not manufactured to the tightest of tolerances or am I doing something wrong? How much are you guys bumping your shoulders? Do you look for a little more resistance camming the bolt to decide on how you set your die?

Thanks,

ST.243

GunBum · Aug 29, 2018

I don't touch the shoulder at all. At least on brass for rifles that I'm trying to neck size only. I've never had difficulty closing a bolt on a neck sized case.

John from MD · Aug 29, 2018

Are you making your own cases or buying them? Is the rifle new or rebarreled?

4g64loser · Aug 29, 2018

This could be due to several things. I tend to bump very little, if any, on my standard chamberings. Those that I do bump, i generally use a Forster neck bushing bump die (223 and 308, with their lame shoulder angles, come to mind). A case that is difficult to chamber after being bumped .002 or more should be VERY carefully measured for expansion at the web area. Your OP does not mention what type of die you are using but, if you are using hot loads, a body sizing operation may be in order. If you are using FL dies (not ideal for what you describe), you will not be able to separately control body and neck sizing. If you are using a neck bushing die and a separate body die for the body/shoulder operation, that is the ideal setup. In my limited experience, the 284 case does not tend to stretch a great deal unless it is loaded FAR beyond SAAMI pressure limits or is overly sized. It is not as stable as my Ackleys but I rarely trim the cases when compared to other, more conventional, cases. A casting of your chamber with CerroSafe would be ideal to sort out the issue.

Pinecone · Aug 29, 2018

Just to make SURE, you are stating with cases fired in THAT rifle?

Then you measure, and then set die to bump the desired amount for the fired case measurement.

John from MD · Aug 29, 2018

I second the casting with Cerrosafe.

Caeb75 · Aug 29, 2018

Honestly the only rifles I "bump" shoulders on are semi autos where I am trying to squeeze every bit of accuracy but the case still needs to be full length sized. I will bump the shoulder back .002-.004 but full length size the body.

For bolt guns, I neck size only. TBH, I fire form virgin brass before I even load it.

Screwtop.243 · Aug 29, 2018

4g64loser said:
This could be due to several things. I tend to bump very little, if any, on my standard chamberings. Those that I do bump, i generally use a Forster neck bushing bump die (223 and 308, with their lame shoulder angles, come to mind). A case that is difficult to chamber after being bumped .002 or more should be VERY carefully measured for expansion at the web area. Your OP does not mention what type of die you are using but, if you are using hot loads, a body sizing operation may be in order. If you are using FL dies (not ideal for what you describe), you will not be able to separately control body and neck sizing. If you are using a neck bushing die and a separate body die for the body/shoulder operation, that is the ideal setup. In my limited experience, the 284 case does not tend to stretch a great deal unless it is loaded FAR beyond SAAMI pressure limits or is overly sized. It is not as stable as my Ackleys but I rarely trim the cases when compared to other, more conventional, cases. A casting of your chamber with CerroSafe would be ideal to sort out the issue.

I'm using a Redding Type S full length bushing die with a .291 bushing. I would not consider the load particularly hot (52.3 grains H4831 under a 130 Accubond) and I've got about 6 cycles on the brass (Nosler) with a trim maybe every other time. At any rate, the rifle shoots very well, so I'm not overly concerned about it. I will look at web expansion, however to see if there appears to be anything untoward going on. Thanks.

Speed3 · Aug 29, 2018

I usually try to bump 2 thou, or enough for the bolt to close easy. What I've found is, I get vertical stringing if the shoulder isn't bumped back enough(guessing pressure increases).

Going 5 thou isn't horrible, it just over works the brass, make sure to anneal frequently.

John from MD · Aug 30, 2018

A trim every other loading seems excessive to me.

Speed3 · Aug 30, 2018

John from MD said:
A trim every other loading seems excessive to me.

For my target gun, I trim every single time I fire.

GUNSnROTORS · Aug 30, 2018

John from MD said:
A trim every other loading seems excessive to me.

True.

ST.243, I'm assuming this brass is fire-formed in this same chamber, and is always used in this same chamber?

In answer to your question, 0.002 here. Sometimes more, but never less. Will always stop hunting for improved accuracy when function begins to suffer.

Screwtop.243 · Aug 30, 2018

GUNSnROTORS said:
True.

ST.243, I'm assuming this brass is fire-formed in this same chamber, and is always used in this same chamber?

Yeah, it's a new rifle (Savage 110) and the brass started out as new Nosler brass, dedicated to the same chamber. I got 6 cycles on my first 20 pieces and they are running strong. I've had no signs of overpressure in multiple charge ladders so far. I'm going to the range again and I'll go through the shoulder bumping routine after I fire these, targeting a .002 bump. I'm beginning to think I may have made an oversight with something here.

4g64loser · Aug 30, 2018

OK, using a FL size die set up for bushings instead of doing the job with two separate dies (neck bushing and body) can induce a slight problem in the neck shoulder junction area. I have sometimes experienced this using Forster neck bushing bump dies on unturned necks. The bushing, by its nature, leaves a small amount of the neck unsized, even if you bottom out the bushing in the die recess. If you do not bottom out the bushing (minus the quarter turn backoff to allow for bushing float, of course) you leave a greater portion of the neck unsized. This can allow brass to build up (the dreaded doughnut, but worse if left unchecked). The fact that you must trim your cases every other firing in a 284 based chambering would concern me where it my rifle. Of factory (non improved) cases, the 284 is one of the most stable. Your load does not sound overly warm in a Norma chamber. The old Winchester wildcat chamber I have no direct experience with. In any event, I believe savage chambers for the Norma print.

The surest way to confirm your pressures without lab test equipment is to measure the web area before and after firing each case, recording the measurement. I dot the case where I put the micrometer so that my data is as consistent as possible. I doubt your pressure is the issue, however, but it is a very easy check to do. I would double check your die setup as a second step. Once all hardware is known-good, then proceed to the detailed case measurement.

Screwtop.243 · Aug 31, 2018

4g64loser said:
OK, using a FL size die set up for bushings instead of doing the job with two separate dies (neck bushing and body) can induce a slight problem in the neck shoulder junction area. I have sometimes experienced this using Forster neck bushing bump dies on unturned necks. The bushing, by its nature, leaves a small amount of the neck unsized, even if you bottom out the bushing in the die recess. If you do not bottom out the bushing (minus the quarter turn backoff to allow for bushing float, of course) you leave a greater portion of the neck unsized. This can allow brass to build up (the dreaded doughnut, but worse if left unchecked). The fact that you must trim your cases every other firing in a 284 based chambering would concern me where it my rifle. Of factory (non improved) cases, the 284 is one of the most stable. Your load does not sound overly warm in a Norma chamber. The old Winchester wildcat chamber I have no direct experience with. In any event, I believe savage chambers for the Norma print.

The surest way to confirm your pressures without lab test equipment is to measure the web area before and after firing each case, recording the measurement. I dot the case where I put the micrometer so that my data is as consistent as possible. I doubt your pressure is the issue, however, but it is a very easy check to do. I would double check your die setup as a second step. Once all hardware is known-good, then proceed to the detailed case measurement.

I think your assessment is very plausible and I think I understand what's happening now. I think it's the bushing float, as it is evident after the resizing step how the bushing is leaving around .02 of the neck unsized. I get this with a "back-off" of about 1/12th of a turn on the decapping stem. That translates into 20 thousandths of "Slop" at the bearing surface of the top of the unsized portion of the neck (at the throat) with the actual shoulder/body datum line, correct? It would almost seem that by turning the die down, I'm bumping the bushing portion of the neck while at the same time bumping the shoulder?

I did check with my Sinclair shoulder bumping comparators and fired cases were 1.785 and I pretty much had to bump them back to 1.781 for easy bolt camming.

All this said, I don't turn necks or sort cases for neck wall thickness uniformity so maybe these are also contributing factors. At the end of the day, the rifle shoots 1/4 to 1/2 MOA so I'd like to think I'm doing something right. Thanks again!

4g64loser · Sep 1, 2018

Always glad to help if i can. If the rifle is running sold half or better, in that chambering, I'd tune the sizing til you are happy and just go with it. One reason I advocate for separating the neck and body operations is what you are experiencing. In SOME neck bushing dies, you still cant fix the "bottom out" issue and don't get full sizing to the neck shoulder junction. I've been known to address that by chucking said die into a lathe and taking some off the bottom so that I can run the bushing to the shoulder if i so choose. This IS NOT required for accurate ammo production. It simply annoys me that I can't control sizing as I see fit.

I'm glad to hear that rifle is a shooter. The bullet on target is the truth.

Shoulder bumping question

The #1 community for Gun Owners of the Northeast

Member Benefits:

Ouch...that thing kicks

Active Member

American Patriot

Bad influence

Ultimate Member

American Patriot

Full fledged member

Ouch...that thing kicks

Ultimate Member

American Patriot

Ultimate Member

nude member

Ouch...that thing kicks

Bad influence

Ouch...that thing kicks

Bad influence

Users who are viewing this thread

Log in

Forum statistics