Shoulder bump

[dbaird]

How far do you normally set the shoulder back on a single shot rifle?

 

[47WillysGuy]

How far do you normally set the shoulder back on a single shot rifle?

2-3 thousands and the bolt minus firing pin drops freely

 

[jepp2]

How far do you normally set the shoulder back on a single shot rifle?

0.001 - 0.002" from the length you can feel bolt contact.

Depending on how hot your loads are, it can take multiple firings for the brass to be the chamber length. So if you don't know the length for bolt contact, you could be setting the shoulder back much further than you need.

 

[searcher]

To expand on the above posts - you might need to fire your brass once to several times in order to just get your shoulder pushed forward enough to feel a bit of resistance when closing your bolt. Only once you feel that resistance do you begin to push the shoulder back incrementally in .001" or so moves till the resistance is not felt with the bolt dropping all the way to closed position. THEN bump it another .001" to .002" as others also noted. Going .001" is usually great if you just annealed the brass as there will be little spring-back when sizing- otherwise .002" as more spring back will be expected. Some adjust to feel just the slightest "crush" just before the bolt reaches the fully closed position. Sometimes that provides the optimum accuracy in a given rifle - sometimes a few .000 "slop" does best. Experiment between the two. If it is a hunting rifle, I'd go about .003" set back and call it good.

 

[mikecr]

1 to 1.5thou for same day use.
2thou for stored ammo.

 

[JFrank]

How far do you normally set the shoulder back on a single shot rifle?

I set the die so my rounds chamber freely about.0035

 

[JEFFPPC]

.001 to .002, stripped bolt requiring a very light touch to fully close. As mentioned above if you do this with a new or once fired cases you will need to redo it after case is fired about 4 times ot till it is fully expanded to your chamber.

 

[savageshooter86]

Take firing pin assembly out of bolt. And bump shoulder back little at a time until when chambering sized case the bolt falls freely on its own. Mine is about 2.5 thou bump to accomplish this.

 

[INTJ]

2.5-3 thousandths. Tight fitting brass is not good for high accuracy applications.

 

[Ccrider]

2.5-3 thousandths. Tight fitting brass is not good for high accuracy applications.

Interesting observation. What pact does too tight have on accuracy. It's ot better to be too lose than too tight?

 

[mikecr]

Is there logic behind evils of tighter head spacing?
What would the problem in it be?

 

[D-4297]

Let's bring the discipline ; caliber , and even the load into the discussion , so we can give the OP some solid , useable information . Many F - TR shooters ( .308 ) only "Bump" their brass .001 , after it has been "cycled" two , three , or more times . And annealed at least once or twice . Some anneal after every firing , so there is no real hard and fast "Rule" to doing this process . My dies are set to bump .001 after every firing now , and the added benefit is that I very seldom have to trim my brass anymore . Maybe every six or seven firings . With a new barrel ; I check my throat length about every 150 - 200 rounds , and check my brass after every firing to see if my chamber is changing , and allowing my brass to change dimension . Guys that shoot .284's , and .300 Win use more Bump , than those of us shooting .308's ....For obvious reasons . And even though I only bump down .001 , I don't get any stiff closures , or hard lifts .

 

[mikecr]

INTJ, would you suggest that D-4297 needs head spacing in excess of his for high accuracy?

 

[INTJ]

Interesting observation. What pact does too tight have on accuracy. It's ot better to be too lose than too tight?

In LR BR, where we usually need to shoot 2" or better aggs to win at 600 yds and 5" or better to win at 1000, the trend is to have MORE clearance between case and chamber, not less.

Many of us run .003-.005" of neck clearance, .002-.003" of shoulder bump, and sometimes even use a small base die. One thing this does is ensure smooth cycling of the action. Smooth cycling is critical to having reliable tracking so all shots can be quickly fired in the same micro-condition.

At first I thought that this was a simple matter of sacrificing a little pure precision in order to mitigate the much larger effects of the wind. However, many think that the looser clearance actually improves precision. I have certainly not seen anything in my tuning and competing that shows less clearance is better.

There was a similar discussion on this topic in the Gunsmithing forum, and I have been thinking as to why more clearance could result in tighter group. It's easy to understand why smooth tracking and rapid strings to keep all shots in the same micro condition would help. The wind is a tough opponent.

As to why pure accuracy might be improved, some think the slightly expanding brass has a dampening effect on the variations in expansion as the round is fired.

Of course, with more clearance, the bullet is not aligned as well with the throat and we all know that is critical. However when we think about the firing process, the case expands to fill the chamber before the bullet leaves the case neck. The fully expanded case allows perfect bullet alignment before the bullet starts moving.

Now maybe a max spec chamber and min spec brass may not allow full alignment before the bullet starts moving, so we do find an accuracy improvement by tightening that up. It's just that when we go for a very tight fit we lose the dampening effect of the brass slightly expanding.

I am not sure. I do know running more clearance than we used to results in smaller groups.

 

[INTJ]

INTJ, would you suggest that D-4297 needs head spacing in excess of his for high accuracy?

It is certainly worth a try.

 

[Doug Beach]

Upon being struck by the firing pin, the chambered round moves forward, until something stops it. A looser fitting case is not sitting in the bottom of the chamber when it fires.

 

[Oleg S]

2.5-3 thousandths. Tight fitting brass is not good for high accuracy applications.

^^^^ this is it

 

[JFrank]

Here’s a question For those whom claim to only relocate the shoulder .001 with success; Are you starting from a fully fire formed piece of brass with hard bolt closer taking a measurement than adjust your die to minus .001 ( barely a human hair) run your case through and have it cycle freely in your chamber?
Seriously’ I wish to know...
Thanks
J

 

[mikecr]

When it's time to bump you can feel interference fit with bolt closure. Here I take a measure with a shoulder gizzy at assumed 0-HS. Then with a film of lube on case, I adjust my body die down trial & error, creeping into .001 of bump after spring back. Then wipe off the case and chamber it. If there is any interference I can feel it right here. I may have to creep into another .0005 bump for what I feel is freely chambering(if assumed 0-HS was actually negative HS).
I log the gizzy measure on this, and I keep it & the set die & the shell holder used together as a pair for that chamber.

Now that little bumping kit could never be trusted to nail every single case right on the money. Some cases just have personalities about taking bump. This is why I absolutely hate shoulder bumping. To do 50 cases I will have to creep into my bump for every single one, going thin to thicker with lube film on the shoulder (not a die adjust)..
If I have to go 45, 60, or 90 deg shoulders with my next chambers until eliminating the need for bumping, it's worth it.

I understand that a chambered pressure point from interference fit affects results, so while I'm so close to that it has to be consistent. And I understand that case expansion on firing takes energy from pressure peaks to make them a bit forgiving. But forgiving in every sense applies only to the inconsistent, and I load develop with ammo built consistent.
I choose tight on everything, so that everything IS consistent, and every piece of brass I make -lasts forever.
I'm a reloader who is no more convinced that sloppy is good for ammo, than sloppy is good for racing engines.
That's just me I guess.

 

[Hohn]

If the case chambers cleanly, it doesn't need bumping. Then again, your die shouldn't touch the shoulder if the case already chambers easily.

It makes sense to me that if you have a tiny bit of negative headspace (i.e. a tiny bit of bolt drag on chambering), then this compression will center the front end of the case on the tapered shoulder. Cone on cone centering. The back of the case might not be perfectly centered, but I don't really care about that. The firing pressure will equalize it out.

It's a fine line to walk, but I FL size every time to the longest die setting for headspace that I can chamber in my rifle. That means that normal case to case variation at times will cause some to chamber easily and others will have some bolt drag. (I don't have an annealing setup yet).

Once i set my sizer for a given headstamp in my chamber, I don't move it.