Shoulder bumping question

[762willdo]

Has anyone tried taking 5 cases with the shoulder bumped 001.5and 5 case with the shoulder bumped .002 and fired them on paper to see if there is a POI change…….? I ask because i cull the cases by the bump and I’m wondering if I wasting time………

 

[GLShooter]

A difference tha5 small has never caused me issues.

 

[Bill Norris]

Doubtful you will see a difference with .0005 bump.

 

[DLT]

I have seen .250” good groups with bad bumps and bad groups with a perfect bump.

 

[DaveTooley]

I sleep soundly at night not worrying about shoulder bump.
The bolt has to operate freely. That's about it.

 

[LHSmith]

How would you measure it. Calipers are only accurate to +/- 0.001" . You need a decent micrometer to measure more precisely.

 

[K22]

How would you measure it. Calipers are only accurate to +/- 0.001" . You need a decent micrometer to measure more precisely.

What Mr. Smith said.

In addition, operator technique variation will cause some measurement variation. Also, depending of the bump gauge used, some have interfaces with inserts and if not aligned the same way each time this can create another source of variation. If your mounting and dismounting the bump gauge before and after each loading session this can create another source of variation. The good news is that I've never seen any difference on target from bumps ranging from "0" to an unintentional bump of .003" in some of my most accurate bolt rifles. So, I doubt a .0005 variation would have any affect, assuming you can measure to that level of precision and / or bump repeatedly to that level of precision.

 

[J.d. Popkes]

What Mr. Smith said.

In addition, operator technique variation will cause some measurement variation. Also, depending of the bump gauge used, some have interfaces with inserts and if not aligned the same way each time this can create another source of variation. If your mounting and dismounting the bump gauge before and after each loading session this can create another source of variation. The good news is that I've never seen any difference on target from bumps ranging from "0" to an unintentional bump of .003" in some of my most accurate bolt rifles. So, I doubt a .0005 variation would have any affect, assuming you can measure to that level of precision and / or bump repeatedly to that level of precision.

.003 bump variations don’t matter on paper?

What distance are we talking?

 

[ebb]

How would you achieve it, let alone measure it. Even under the best of conditions and leaving the cases in for a 5 second dwell time and rotating them 180 % and sizing again with the 5 second dwell I still get cases that a little different than the rest.

 

[JFrank]

Has anyone tried taking 5 cases with the shoulder bumped 001.5and 5 case with the shoulder bumped .002 and fired them on paper to see if there is a POI change…….? I ask because i cull the cases by the bump and I’m wondering if I wasting time………

I’ve separated ( culled) cases for a lot of different reasons but never for a slight difference in base to shoulder.

 

[nmkid]

.003 bump variations don’t matter on paper?

What distance are we talking?

Working on cases for my new 243AI I, (not on purpose) mistakenly sized 50 cases .003 bump. The rifle is shooting less than .500 consistently. The best 3-shot groups are .152 and .272. I'm not moving that die!

 

[Ccrider]

I want the difference to be in the plus side of the equation rather than the minus. .0005-.001 more is not going to hurt anything. Depending on how much clearance you are creating, .001 less can interfere with bolt lift.

 

[JMayo]

I don't think shoulder bumping & accuracy run hand in hand.
Shoulder bump is about smooth operation of the bolt, consistent ignition of the primer
& Wear and tear on the case.
that's about it as far as I'm concerned.

 

[Webster]

Has anyone tried taking 5 cases with the shoulder bumped 001.5and 5 case with the shoulder bumped .002 and fired them on paper to see if there is a POI change…….? I ask because i cull the cases by the bump and I’m wondering if I wasting time………

By culling do you mean throwing away good cases? All the top competitive shooters say bump 0.002". No one recommends 0.0015" bump. Just bump 0.002" and forget about it. The group size on the target is the only criterea that matters. Your die probably won't bump every case the same exact amount. This is normal. Most of use don't have a serious competition quality rifle and top shooting skills. This means we cannot shoot good enough to see what effect small changes make. My rifles average about .350" groups. I accept this as what I can live with. The biggest improvement I ever found was finding the bullet that my barrel liked. Very expensive to try a lot of different powders and bullets. I am happy shooting the same bullet and powder till I die.

 

[LHSmith]

Just like some barrels favor a certain seating depth, some barrel/ action combinations like slight resistance on bolt closure vs. where the bolt just free-falls. You don't measure this stuff-you let the gun tell you.
Edit- Speaking strictly about full blown competition rifles where results are measured in the thousandths.

 

[BoydAllen]

Has anyone tried taking 5 cases with the shoulder bumped 001.5and 5 case with the shoulder bumped .002 and fired them on paper to see if there is a POI change…….? I ask because i cull the cases by the bump and I’m wondering if I wasting time………

You are wasting your time.

 

[K22]

.003 bump variations don’t matter on paper?

What distance are we talking?

200 yards on paper - longest range I have access to for paper punching.

Varmint / Predator hunting - up to 300 yards - they never knew the difference between a .001 and .003 bump.

I do not intentionally bump to .003" but sometimes on some lots of brass, I will get one that occasionally bumps more than the others. I only bump, when necessary. My target bump is .001 to .002 max.

 

[J.d. Popkes]

200 yards on paper - longest range I have access to for paper punching.

Varmint / Predator hunting - up to 300 yards - they never knew the difference between a .001 and .003 bump.

I do not intentionally bump to .003" but sometimes on some lots of brass, I will get one that occasionally bumps more than the others. I only bump, when necessary. My target bump is .001 to .002 max.

In my experience, it makes a noticeable difference. I think whether you bump 1 or 5 is irrelevant, but one that’s 1 will not have the same poi as one bumped 5 of more. Probably not prairie dog critical.

 

[J.d. Popkes]

Inconsistent shoulder bumps are directly affecting ignition timing, if I understand it correctly. I’m not a scientist but I do know it matters, to me.

I think….. that all brass prep matters. From trimming every time, to a good and consistent chamfer/debur(Henderson), annealing, bumping, carbon in neck or neo lube or that Redding media stuff, and wait for it…… primer pocket cleaning. I can’t seat primers consistently in dirty pockets. According to my measuring tools.

That advice is worth what you paid for it

 

[K22]

In my experience, it makes a noticeable difference. I think whether you bump 1 or 5 is irrelevant, but one that’s 1 will not have the same poi as one bumped 5 of more. Probably not prairie dog critical.

I'm sure you're correct especially if your experience indicates as such. Those in the ultra-precision game of benchrest and long-range precision shooting attempt to keep everything as consistent as possible and go to extra lengths to do so. I imagine, small variations can make a big difference in their game.

My needs are not as precise. Of course, I want the most accurate reloads I can produce but I balance that with trying to keep my reloading process as simple as possible. I have not noticed any POI changes (within my normal aggregates) shooting at 100 and 200 yards on paper or at varmints / predators up to 300 yards with bump variations of + or - .001, even an isolated occasionally .002 variation.