Hard Chambering. . . Non-perpendicular Bolt Face


PDA






edwardware
October 31, 2011, 10:01 PM
A question for those with lots of experience inside a bolt action rifle. . .

I'm (attempting to) reloading .270 Win for my '70s era Ruger M77. Using once-fired Federal brass, I observe an interesting phenomenon. The factory rounds chamber with ease, and extract with ease. If I take a just-fired case, and rotate it, it chambers hard (lowering the bolt handles requires deliberate force, call it 20#). As I keep rotating it and trying to chamber, I find that one particular angular orientation is easy, and all others are hard.

The same goes for my neck-sized reloads. They chamber hard, but as I rotate them before chambering, I find an easy orientation. Full sized cases chamber just like factory ammo; easy. The hard-to-chamber neck sized reloads as still quite accurate, and don't show any pressure signs. Charges are the starting charges for IMR-4320 behind a 130gr Interlock.

My first guess is that my bolt face is not perpendicular to my chamber. Is this reasonable? Is it likely? What else could cause this? How do I fix it?

I'd rather not FL resize all my brass for this rifle, and I can't see paying hundreds for a smith to drop the barrel and true the bolt face.

Suggestions?

If you enjoyed reading about "Hard Chambering. . . Non-perpendicular Bolt Face" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
918v
November 1, 2011, 03:24 AM
Your first guess is correct, and it is the reason why neck sizing for factory rifles is a pain. Factory rifles are seldom square and bolt faces have runout. It could be .001" or .010". When you fire a round, the case head will mold itself to the bolt face. Unless you reinsert the case exactly the same way you'll experience hard bolt closing.

You have a few options: blueprint the action- this will square the bolt face as well as the bolt lugs and the lug recess. Or, index the cases in the chamber- this is a pain in the arsch because the bolt will want to rotate the case when closing. Or, FL size leaving about .003" of headspace.

DANS40XC
November 1, 2011, 03:48 PM
Chamber is not round/concentric,hence the need to index fired brass to the chamber.
Nothing to do w/ bolt face not being perpendicular to Bbl.
Indicate the case head to verify instead of assuming.
F/L size the brass & shoot!!

SlamFire1
November 1, 2011, 04:11 PM
What about the possibility of an oval chamber?

Gun drilling never provides a perfectly straight tube, the hole always has some curvature.

You stick a straight chamber reamer in a curved hole you will get an oval chamber.

fguffey
November 1, 2011, 04:14 PM
Edward,

http://www.ruger.com/products/m77Hawkeye/index.html

This is the reloading forum, not easy to get something like help past past the brain trust , but that has never stopped me before, not sure why a smith would need to remove the barrel if the problem is the bolt face.

Nothing about head space hangs me up. if the correction requires truing up the face metal will be removed, removing metal from the bolt face will increase head space (length of the chamber from the bolt face to the shoulder of the chamber). You know the case must be indexed to chamber after firing., you could start sizing the case by adjusting the die to the shell holder with a feeler gage starting with .004 thousands and continue reducing the gap until the case will chamber when indexed .180 degree off, the thickness of the gap should give you an ideal the amount of sizing required to chamber the case.

Big problem with full length sizing, the case between the case head and case body will be compressing on one side. Attempt standing the case up against a square surface and rotate, attempt ‘V’ blocks and a comparator/run-out/dial indicator.

When replacing a bolt to correct a problem most are propelled into the twilight zone, I first determine the length of the chamber, when determining the length of the chamber a go-gage is useless, everyone???? knows the go gage will allow the bolt to close, but, they do know by how much. and that is the reason I determine the length of the chamber first in thousands.

It is very unlikely I would replace a bolt to correct a problem like too much head space or not enough head space, but, if I did I would determine the distance from the bolt face to the back of the locking lugs (simple tool), problem, I could not find anyone that that understands the technique/procedure. Most want the rifle shipped to them or they want to sell 5 bolts in the hope one will increase and or decrease the effect the bolt will have on head space.

Again, a friend was building a 1903 Rock Island period correct 1911 rifle with a straight handle, he has no less than 30 go-gages, none of the gage gave him the answer he needed, he was trying to work with a dysfunctional forum, you know, well there is this ‘datum line’ up there etc.. anyhow I informed him “This is your lucky day”, he had .0075 head space, with a spread of .00025 thousands between the length of 20 New, minimum length, full length sized rounds of R-P 30/06 rounds his head space for 1 box of new Remington ammo was .0075 + or – .00025. He had/has no less than 80 Springfield bolts, I have no less than 40, I offered to check the effect each bolt had on offsetting head space, but none of the bolts had a straight handle.

Moving the bolt face back increases head space, to correct head space, the barrel can be moved back. Head space does not hang me up, again I have a M1917 with .016 thousands head space and no, there is no gage that is + .016 thousands, the field reject gage is .014 thousands longer than a minimum length/full length sized case. And we all know the field reject gage will allow the bolt to close on a chamber with a chamber that is +.014 longer than a minimum length chamber to infinity, problem very few can determine '”by how much”.

F. Guffey

fguffey
November 1, 2011, 04:35 PM
and if the chamber is oval the case will chamber twice when rotated 380 degrees, Wayne, try to lay the case down on a flat surface and roll it, there could be a bulge, the case could be oval, if it is oval the case will have two eccentrics.

Anyhow a friend sent a Ruger back to Ruger, as my friend tells the story it was the most accurate rifle he ever owned, he contacted Ruger, after Ruger heard the story he asked my friend, “Are you sure you want that Accurate rifle fixed” and my friend said “yes”, and now my friend talks about the accurate rifle he ‘you-sta’ own.



F. Guffey

gamestalker
November 1, 2011, 07:39 PM
If the bolt face or lugs are not square you could get the same effect. Also, it is more likely because it is more common that the problem is related to lug or bolt face. It unusual for a chamber to come out egg shaped, very unusual.

I would consider all of what Fguffey has to say on the matter, he is well versed in this area. Also, this isn't something I've never seen with standard production bolt action rifles, which is one of the reasons serious precision reloaders and bench rest shooters drop so much money on custom actions, or take the time to preperly tune an action that has enough to work with.

918v
November 1, 2011, 08:36 PM
Chamber is not round/concentric,hence the need to index fired brass to the chamber.

Concentric with what? The bore? What does that have to do with anything?

edwardware
November 1, 2011, 09:20 PM
@918v: I considered the possibility that I had an oval shaped chamber. I don't have a 0-1 mic, but using a caliper and spinning the once-fired brass in the caliper jaws, it feels and appears perfectly round. Also, the egg shaped chamber would seem a less likely error than a canted bolt face.

@fguffey: I guess I had assumed that straightening the bolt face would require dropping the barrel and blueprinting the whole thing (kinda expensive for a $400 arm). From what you've said it sounds like it might be possible to just true the bolt face to the bolt body on a lathe (instead of truing it to the receiver threads with the thread-in tool). Is that what you're thinking? I understand that such a correction might run the headspace over spec, but then again it might not.

At the end of the day, this rifle runs just under 1 MOA with cheap Federal rounds, and my handloads (hard chambering or not). Maybe I should be content. . .

918v
November 1, 2011, 09:59 PM
Truing the bolt face will increase headspace, but if you can always set the barrel back to compensate.

The easiest solution is to size the body with a body die and the neck with a Lee collet neck die ;)

fguffey
November 2, 2011, 08:12 AM
Edward, nothing like a set-up table, last word (spot-on) indicators, squares, ‘V’ blocks etc.. If the head of the case is not true with the case body the case will not stand up straight, flat surface, upright ‘V’ block clamped and a dial indicator set up, then rotate the case, I can do the same thing with less by substituting blocks with a feeler gage and a flat surface.

Again, there is the go-gage, there is the no-go gage and finally, the field reject-beyond gage. If the bolt face requires truing metal will be removed, as you know removing metal from the bolt face will increase head space, back to ‘no shortage of tools’ I determine the length of the chamber first, the 270 W is an easy chamber to work with because of the available 280 cases, moving the shoulder back to fit is easier than fire forming, that method (fire forming) is used by those that can not figure how to get the shoulder forward by any other method.

If you were able to measure the length of a fired case from the head of the case to it’s shoulder and was able to rotate the case while measuring you should be able to get two measurements while rotating the case, the difference in the two measurements should give you an indication as to how much metal would be required to true the face of the bolt.

It does not seem fair, all my presses have threads, all of my dies have threads meaning my press and dies were designed to be adjusted to the shell holder, I have short chambers and long chambers, that would be chambers that are too short for a go-gage and too long for a field reject gage, for a 270 chamber that would be a .026 thousands spread from –.012 thousands shorter than a minimum length case to +.014 thousands longer than a minimum length case from the head of the case to the shoulder of the case.

Moving the barrel back is an option, not necessary, the brain trust never mentions case head protrusion, Hatcher is said to have speculated ‘case head protrusion’ could be the cause of all this stuff coming apart’. I have found 03 Springfield's to have .090 thousands when measured from the bottom of the extractor groove to the head of the case, I have found 98 Mauser types to be .110 + or – very little, back to moving the barrel back, your bolt face could be forward on one side and set back on the other giving you a reading of + and – from 0, truing the bolt face up could only require .003 thousands, that would give you .008 thousands head space, .001 short of a no-go gage length chamber and when forming 280 Remington cases for your 270 chamber you would be moving the shoulder back on the 280 R case .043 thousands for .000 head space.

I off set the effect the chamber will have on the case when fired by off setting head space with the case.

F. Guffey

fguffey
November 2, 2011, 08:30 AM
“such a correction might run the headspace over spec, but then again it might not”

I have a M1917 with .016 thousands head space, that is .016 thousands longer than a minimum length case, .009 thousands longer than a go-gage length chamber, .002 thousands longer than than a field reject length chamber, my favorite cases for that chamber are cases that have been fired in trashy old chambers and new/once fired 280 Remington cases. When sorting cases I have purchased from the range I measure the length of the case from the head of the case to it’s shoulder, once I find cases that are long I apply the leav-um policy, I leav-um the way I found-um. Again, there are fire formers, then there are formers.

I prefer moving the shoulder of the case back to form, others have no choice but to make a trip to the range and fire to form.

F. Guffey

gamestalker
November 2, 2011, 10:09 PM
Although I agree 100% with Fguffey explanation, I do disagre that most factory chambers are not going to function with neck sizing, as was stated by 918V. I have been necking my brass forever in standard production actions and have yet to encounter a problem that would indicate any of my chambers are out of round. If I ever ran into one that gave me that problem, I would not hesitate to ship it back for replacement, or if possible, repair.

Most of my high powered rifle belted magnum brass will run 12-15 cycles. My .270 win, .280 rem, 30-06 brass will go 20+ cycles before being scraped. The nice thing about those cartridges is I always have one chamber that is a bit deeper to the shoulder and will transfer from one to the other by pushing the shoudler back to fit a particular action. .280 to .270, or 30-06 to .270 and so on. And all of it has chambered without resistence for the first 6 or 7 reloadings at which point I set the shoulders back .002" and then go another 1/2 dozen cycles before the next shoulder job. Yes, there are other more precise ways to do this, but for the common reloader who just wants to extend brass life while getting excellent groups, a properly adjusted FL die will get the job done well with .001" increments using a set of feeler's & dial caliper.

918v
November 3, 2011, 01:32 AM
In every factory rifle I have loaded for, the bolt became increasingly harder to close with every neck sized reload. The bolt became a SOB after the fourth or fifth reload. This is not an issue in my accurized guns.

edwardware
November 3, 2011, 08:36 AM
gamestalker: I like the sound of that plan, but how do you set the shoulder back without partially sizing the body?

918v: I haven't noticed any issues caused by the hard chambering, but it would be nice to fix it if it's practical, hence my questions.

USSR
November 3, 2011, 10:39 AM
...how do you set the shoulder back without partially sizing the body?


The only way that I believe it could be done is with a Forster die that is set up as a necksizer that bumps the shoulder as well. Any time you are using a FL die or body die, no matter how you set it up, you are sizing the body at least somewhat before the case is far enough up in the die to bump the shoulder back.

Don

Jim Watson
November 3, 2011, 10:54 AM
I'd rather not FL resize all my brass for this rifle, and I can't see paying hundreds for a smith to drop the barrel and true the bolt face.

Suggestions?

What is your objection to full length sizing? Brass life? Cleaning off the sizing lube? Too many gunzine articles and internet posts about applying benchrest techniques to hunting rifles?

My suggestion: Get over it. Full length size and go shooting.
The guys are willing to spend your money and time on gunsmiths, trick dies, and endless tinkering, but the right answer is to full length size and not worry about it. Of course you will set the die no deeper than necessary to let your wobbly bolt turn without excess effort, but that is just common sense and standard practice.

edwardware
November 3, 2011, 01:01 PM
@ USSR: Yes, that's what I was thinking.

@ Jim Watson: All of the above, plus the extra work of FL resizing. Neck resizing is easy and FL resizing makes me break a sweat. The elegance of neck sizing is appealing even though I haven't produced any measurable improvement in accuracy.

bigedp51
November 6, 2011, 04:41 PM
Before you blame the rifle for your problems don't forget that a brass cartridge case can warp and become banana shaped! If the case has uneven case wall thickness the thin side of the case will expand more and when the brass tries to "spring back" to its original shape it warps. When this happens the base of the case is pushed off center and is no longer 90 degrees to the axis of the bore.

Full length resizing will only make it worse because you are compressing the case and pushing the base of the case even further out of alignment with the axis of the bore. Run out gauges that can be setup to gauge the base of the case are what are needed to "see" and measure this problem.

The National Rifleman magazine printed an article about warped banana shaped cases in the mid 1970s. It is more exacerbated or worse when shooting commercial cases in larger and longer military chambers which causes the brass to stretch and warp even further.

Next time gents don't be so quick to blame the rifle, brass is softer than steel and is the weak link inside your chamber.

Below a .303 British case that is warped and banana shaped due to unequal case stretching. Note the unequal case head separation and how uneven the case has stretched and the "angle" of the separation. (and "why" competitive shooters buy Lapua brass.

http://i122.photobucket.com/albums/o254/bigedp51/bent.jpg

If you enjoyed reading about "Hard Chambering. . . Non-perpendicular Bolt Face" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!