1903a3 headspace issue

[buckeye44]

I have a 1903a3 with a 3-43 remington barrel. The barrel and reciever match to with in one month of production and everything on the rifle appears to remington and correct. The rifle is very clean with correct arsenal stampings for a possible rebuild of some sort. Anyway here is the question what is the maximum headspace allowed? I fired this rifle for the first time the other day and let me say with open sites it will hit a 6''x8'' plate at 150 yards everytime with open sites if you do your part but I noticed that with my reloads the primer was backing out slightly. I thought at first this may be due to a hot load but since these reloads were for my M1 and were a little light I ruled that out right away and even after trying some korean surplus M1 ammunition in it and it did the same thing I came to the conclusion we are looking at a headspace issue. The rifle chambers the rounds fine and extracts and ejects normally. I see no indication of case seperation and I bent a paper clip and felt the inside of the case as well and could feel no ring either. I measured over all length and found the primer to back out on average .008 so what is the conclusion to this I have heard that military tolerance are more open than sammi spec if so is this with in those or am I in need of a gunsmith with some go no-go gauges to make that determination. The ammunition used was also fired in my 1955 springfied M1 and I had no primer issues as well.

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Badger]

Here's a couple of excellent videos that might be helpful ...

Head Spacing (video mini lesson) - AGI Gunsmiths

Regards,
Doug

[buckeye44]

Thanks for the video Badger I can see that from my own inspection and the video that although there is a slight headspace issue the rifle can be fired some what safely. I do reload so I am going to search for a gunsmith to set the head spacing if possible. I dont want early case failures in my reloaded brass to come up

Here's a couple of excellent videos that might be helpful ...

Head Spacing (video mini lesson) - AGI Gunsmiths

Regards,
Doug

[Patrick Chadwick]

with my reloads the primer was backing out slightly.

Your load may be low to the point of being marginal.

If you are full-sizing the cases, and then firing light loads, and there is a head clearance of X thousandths of an inch, then the following happens:

The striker pushes the cases forwards by the amount X.
The striker continues to advance and ignites the primer.
The powder charge is ignited and expands the case enough to grab the chamber wall, but the pressure is not enough to stretch the case and drive the base back onto the bolt face.
The pressure is however sufficient to drive the primer back.
As a result, the primer is backed out by the amount X.

This sequence does not harm the case, and your head clearance is simply the amount by which the primer has been pushed back. But you may notice soot around of the neck, indicating that the powder charge is marginal. If, however, you were to use a full charge, then the case would have been stretched by the amount X, pushing the base back down around the primer, and you would not have seen a backed-out primer.

You may be wondering why I write head clearance, and not head space. Simply because head clearance is the real difference between the shoulder-base length of the actual case and the chamber, whereas head space is the same measurement, but made with a headspace gauge. Since one normally fires cartridges, not gauges, head clearance is the figure that tells you the actual value, as opposed to the (theoretical) gauge value. Real cases have tolerances, so there is no point in aiming for a head clearance of zero, as this could mean that cases from a different manufacturer (or even a different lot) will not chamber properly.

The answer to all this is simple: use an adequate load to ensure proper case expansion and only neck-size the cases, so that after the first firing the cases will have stretched to fit the chamber, less the amount of spring-back in the brass (one or two 1/000 I imagine). Since subsequent cycles are within the elastic range of the brass, the cases will last for many reloads, eventually failing at the neck - which is being continually worked beyond the elastic range. (And bench-rest reloading artists use chambers and bullets sized to avoid even that)

There is only one drawback to this method - since the cases are now "tuned" to fit the rifle, they may not be perfect for another rifle. So if you have more than one rifle of the same calibre, it is very advisable to keep the sets of cases separate and indentifiable (by marking them or using cases from different manufacturers).
This sequence will not have damaged the case in the slightest.

[buckeye44]

Patrick thanks for the reply I am aware of which you speak however the rifle did the same thing with military surplus korean ammunition.This ammunition was on the 8 round clip and was loaded for the M1. I highly considered that which you spoke of to be the issue and I may buy some winchester or remington 30-06 ammunition just to double check. Perhaps the korean ammunition and my reloads are light and causing the problem

Your load may be low to the point of being marginal.

If you are full-sizing the cases, and then firing light loads, and there is a head clearance of X thousandths of an inch, then the following happens:

The striker pushes the cases forwards by the amount X.
The striker continues to advance and ignites the primer.
The powder charge is ignited and expands the case enough to grab the chamber wall, but the pressure is not enough to stretch the case and drive the base back onto the bolt face.
The pressure is however sufficient to drive the primer back.
As a result, the primer is backed out by the amount X.

This sequence does not harm the case, and your head clearance is simply the amount by which the primer has been pushed back. But you may notice soot around of the neck, indicating that the powder charge is marginal. If, however, you were to use a full charge, then the case would have been stretched by the amount X, pushing the base back down around the primer, and you would not have seen a backed-out primer.

You may be wondering why I write head clearance, and not head space. Simply because head clearance is the real difference between the shoulder-base length of the actual case and the chamber, whereas head space is the same measurement, but made with a headspace gauge. Since one normally fires cartridges, not gauges, head clearance is the figure that tells you the actual value, as opposed to the (theoretical) gauge value. Real cases have tolerances, so there is no point in aiming for a head clearance of zero, as this could mean that cases from a different manufacturer (or even a different lot) will not chamber properly.

The answer to all this is simple: use an adequate load to ensure proper case expansion and only neck-size the cases, so that after the first firing the cases will have stretched to fit the chamber, less the amount of spring-back in the brass (one or two 1/000 I imagine). Since subsequent cycles are within the elastic range of the brass, the cases will last for many reloads, eventually failing at the neck - which is being continually worked beyond the elastic range. (And bench-rest reloading artists use chambers and bullets sized to avoid even that)

There is only one drawback to this method - since the cases are now "tuned" to fit the rifle, they may not be perfect for another rifle. So if you have more than one rifle of the same calibre, it is very advisable to keep the sets of cases separate and indentifiable (by marking them or using cases from different manufacturers).
This sequence will not have damaged the case in the slightest.

[Patrick Chadwick]

I must add to my previous posting that, of course, your cases may have stretched a bit, but you cannot know how much. In other words, the head clearance is not X, but X plus an unknown amount. To make an accurate-enough measurement, use the method which was first published by jmoore (if my memory is correct). Take a case that was fired with a full/factory load, where you can be sure that the case was stretched as much as the chamber would permit. Full-size that case, making sure that the die and press are really set correctly. Now partially insert a fired primer into the case, so that it protrudes. Load that case into the rifle, and close the bolt on it, so that the primer is pushed in as far as the bolt face goes. At the same time, the case will have been pushed up to the shoulder in the chamber. If you now remove the case and measure the amount of primer protrusion, you will have a very good measurement of the real head clearance for that type of case in that rifle.

If you perform this measurement with factory-new cases, you may be surprised! I have a strong suspicion that some manufacturers size their new cases to CIP/SAAMI minimum minus a production tolerance. Maybe only one or two 1/1000", but enough to worry those who place too much trust in headspace gauges.

It bears repeating: you will have the best results with just about any service rifle if you neck-size cases that have been fire-formed in that rifle.