M305: case length gauge question

[stevebc]

I'm new to the M305 and to reloading for it. For the first time I've bought a Lyman case length gauge, and the instructions say to make sure the (sized) case head is above the lower step and below the upper step.

I have several old Imperial .308 cases, some Winchester cases, even some Federal.

I sized them, tried them in the gauge and the case heads all seemed to sit a bit high, so I set the die a bit lower, and ran them through again.

Many of the sized case heads are still standing proud of the upper step, but just barely, around .00025 inch. Some seem to sit flush on one side, and just barely proud on the other.

I look at them and think "damn that's close", but my ignorance could get me in trouble here.

My question is, should these cases be considered beyond spec?

 

[yomomma]

Never used one of then. I use a case comparator and a go heads pace gauge. Set up the dies to be 3 thou smaller and never look back.

With the m305 close enough is not good enough when it comes to over sized brass

 

[kward]

you have to trim your cases to achieve the proper lenth.if properly resized the case should plop to the bottom of the gauge.trimming will take care of the stepped side of the gauge

 

[wce323078]

are you checking them with gauge standing on the bench? With mine you have to hold it as the case if it needs trimming can extend out of the case distorting the reading.
Case should just drop in and fall between the grove machined in the gauge. Also if it is good that way flip it over and check the neck it will indicate if needing trimming or not.

I also found if it seems a little slanted resize a couple of times turning the case say 1/3 of a turn. If you do this make sure the case is still lubed or it could get stuck in the gauge. Ask me how I know.

I size before I trim as I trim with primer removed. I don't have a stand alone depriming die

 

[bigedp51]

I'm new to the M305 and to reloading for it. For the first time I've bought a Lyman case length gauge, and the instructions say to make sure the (sized) case head is above the lower step and below the upper step.

Drop in case gauges like your Lyman gauge are designed for a civilian SAAMI chamber and military chambers can have longer headspace settings.

Like yomomma I use a Hornady cartridge case headspace gauge, I simply measure a "fired" case and bump the shoulder back .003.

You will get far more accurate case measurements with the Hornady gauge using a digital vernier calipers than eyeballing a drop in case gauge.

Also with a drop in case gauge many times a fired case is too large in diameter to drop into the gauge, meaning you can't get a fired case length.

The headspace settings for the M14 below are not the same as civilian SAAMI settings

 

[Keithjohn]

Trust the gauge . With that floating firing pin you want error margin (lots). If it fires with the lugs not completely engaged nothing but bad can happen. If they don't pass my Lyman gauge like you describe I throw the brass away or use it in a bolt gun . Use small base dies and #34 CCI primers helps piece of mind . Mines a national match with a tight chamber and doubles are common with factory shells (many brands ) I only use top QC reloads now

 

[stevebc]

are you checking them with gauge standing on the bench? With mine you have to hold it as the case if it needs trimming can extend out of the case distorting the reading.
Case should just drop in and fall between the grove machined in the gauge. Also if it is good that way flip it over and check the neck it will indicate if needing trimming or not.

I also found if it seems a little slanted resize a couple of times turning the case say 1/3 of a turn. If you do this make sure the case is still lubed or it could get stuck in the gauge. Ask me how I know.

I size before I trim as I trim with primer removed. I don't have a stand alone depriming die

I like this idea, will give it a try.

Yes, I'm holding it in my hand and looking at where the head is, so it's not the extra length sitting on a surface that makes it sit a bit high.

kward, I'll be doing the trimming next, for now I'm just seeing what brass passes the gauge.

Thanks to all for your replies- I'll err on the side of caution.

 

[Ron AKA]

I like this idea, will give it a try.

Yes, I'm holding it in my hand and looking at where the head is, so it's not the extra length sitting on a surface that makes it sit a bit high.

kward, I'll be doing the trimming next, for now I'm just seeing what brass passes the gauge.

Thanks to all for your replies- I'll err on the side of caution.

I take it that you have this gauge from Lyman?

A quote from the Lyman site:

"Protect yourself and your firearms

To achieve the highest degree of safety and accuracy, Lyman recommends that all bottleneck rifle cases be inspected after resizing to ensure that the proper headspace dimension is maintained. The best way to check this critical dimension is with a Lyman case length/headspace gauge. The reloader simply inserts the case into the gauge to insure that it does not exceed the maximum or fall below the minimum allowable headspace. In addition, the gauge will identify a case which exceeds the maximum allowable case length . Caution: Any case found with excessive headspace should be destroyed immediately."

The concern I have about this is that Lyman has no idea what the size of the chamber is in your specific gun. The only way they could make a gauge like this is to base it on standard SAAMI tolerances, which are frankly quite large. If you have a longer chamber but still within SAAMI specifications, and then you resize the case to minimum SAAMI, you are working the brass a lot, and you are creating significant headspace which has consequences.

The normal practice at least in reloading for precision is to bump the shoulder back 0.001 to 0.002" when you resize. At least in theory that gives you a headspace of about 0.002" or so. However it assumes the fired case was fired in your gun, and that it has resized itself to fully fit your chamber. If you have brass which has been fired from your gun, one trick you can use is to remove the primer, then seat it again with lots of the primer still sticking out. Then chamber that case fully and carefully remove it. The amount that the primer is still sticking out of your case is an indicator of how much headspace you have on that fired case. If it is very small, then that case is a good gauge to use to determine where you stand. If you have a tool to measure headspace this primer method lets you set an absolute standard for your gun for case length (base to shoulder). Then you are not arbitrarily bumping the shoulder back on cases. You are bumping to a standard. You are also not always resizing to SAAMI minimum which could mean your case is way short and headspace is excessive.

Here is a tool to do this kind of thing.

Hornady Headspace Kit

 

[bigedp51]

The normal practice at least in reloading for precision is to bump the shoulder back 0.001 to 0.002" when you resize. At least in theory that gives you a headspace of about 0.002" or so. However it assumes the fired case was fired in your gun, and that it has resized itself to fully fit your chamber. If you have brass which has been fired from your gun, one trick you can use is to remove the primer, then seat it again with lots of the primer still sticking out. Then chamber that case fully and carefully remove it. The amount that the primer is still sticking out of your case is an indicator of how much headspace you have on that fired case.

In a semi-auto it is recommended the shoulder bump or shoulder setback be .003 to .006 and the case diameter be reduced .003 to .005 from fired diameter.

A rifle has headspace and a case when resized will have "head clearance", meaning your use of the word headspace can be confusing to new reloaders.

Your also very good at repeating what you have read in other postings and trying to pass this information off as your own.

Your acting more and more like sunray and multigunner with every posting and being a poser.

Some here may remember my fingers and vernier calipers in the photos below.

At least you didn't copy my photos and use them poser.

 

[bigedp51]

I'm new to the M305 and to reloading for it. For the first time I've bought a Lyman case length gauge, and the instructions say to make sure the (sized) case head is above the lower step and below the upper step.

I have several old Imperial .308 cases, some Winchester cases, even some Federal.

I sized them, tried them in the gauge and the case heads all seemed to sit a bit high, so I set the die a bit lower, and ran them through again.

Many of the sized case heads are still standing proud of the upper step, but just barely, around .00025 inch. Some seem to sit flush on one side, and just barely proud on the other.

I look at them and think "damn that's close", but my ignorance could get me in trouble here.

My question is, should these cases be considered beyond spec?

Any time you are sizing mixed brass the cases will "spring back" at different rates in diameter and shoulder location.

I buy 500 military once fired Lake City 5.56 at a time and size them with a small base die and bump the shoulders back .003 to .004 from their "fired length".

I use redding competition shell holders and making sure the die makes hard contact with the shell holder and pause at the top of the ram stroke to reduce brass spring back.

In order to achieve the correct shoulder bump for your chamber you need to know the "fired length" of the case.

My main point being by using a drop in case gauge there is a possibility of over resizing the case and pushing the shoulder back too far.

Bottom line, knowing the "fired length" is how you set the die for the correct shoulder set back.

 

[stevebc]

I may have got this wrong, but here's what I've done:

I took an unsized fired case, tapped out the primer, and re-inserted it quite proud.

Chambered it by inserting brass in chamber and:
- letting the bolt slam home on it,
- easing the bolt home, then pushing firmly on the op rod until it fully closes.

Either way, the difference I measured was .004

So do I set the die to this fired length brass, then take it down .003 to .004?

Other stuff: I'm using standard RCBS .308 Win dies and my M305 is chambered in .308 Win, not 7.62 x 51, if that helps.

Should I just go ahead and buy some small base dies?

 

[yomomma]

Where to start.

What you did is useless.

Fire a round with the gas valve turned off.
Measure. (See Bigedp51, know your fired case measurments)
Use this measurement as you base.
Adjust dies to be 3 to 4 thousands smaller.

When I dropped in a new bolt I was at 1.361.
I took my shell holder and removed 2 thousands off the top.

She'll holders are the cheapest.

You need a proper tool for measuring.

 

[Keithjohn]

I don't worry about oversizing the brass but I do throw them away after 3 firings ( I have found signs of weak case heads at 4) I feel inside with a bent paper clip on the third regardless also . This gun freaks me out when it double fires and I try to take all measures to make Safty the top priority. The info on m14.ca has a lot of info about the slam fire dangers . As far as accuracy goes shutting off the gas and running it like a bolt gun makes a lot of difference for testing my handloads. Because of my paranoia I use the small base sizes and the #34 primers as well as throwing the brass after 3 firings with IVI brass also as it is thicker . I did not know what I was getting into when I bought this gun but I'm learning and having much more fun thinking I've taken all precautions that I know of
And I do now have the Forster datum tool but find different measurements after firing , not as much using the IVI brass but still some

 

[Pr589]

Stevebc - You can use your Lyman gauge and a caliper to get a fairly good measure of your excess headspace. Use a case fired with the gas turned off (extraction can stretch the brass), insert it into your gauge and measure from the top of your case gauge to the bottom of the case. Now measure the length of the case gauge and subtract it from your previous measure. The only tricky part of measuring "case headspace" is the fact that you have to measure from the datum point of the shoulder. Anything (e.g. Your case gauge) with the right diameter hole will work.

Alternatively you can just use your first measurement as a reference when you are testing your sized cases. Just make sure that your sized cases are 3-4 thou shorter than the reference.

I usually just size to maximum SAAMI spec and have gotten 10+ reloads out of most of my M305 brass. After 10 reloads it goes into a bin to reload for bolt guns. I've only had 2 case head separations in over 3,000 rounds (the separations were on 2nd firing). The decision to size to SAAMI max for the M305 was a) my tests showed no differences in accuracy between minimally resized brass and that sized to SAAMI max, and b) my friends and I were at the time trying lots of loads and sometimes swapping reloads between rifles and the risk of one of us blowing up a gun was not one I wanted to take.

Check the 1.5 MOA Challenge in the Main Battle Rifle forum to get some ideas about what loads and tweaks are working for other folks.

 

[Pr589]

This gun freaks me out when it double fires and I try to take all measures to make Safty the top priority.

Keithjohn - If your M305 is double firing make sure that you don't have a defective trigger. I've seen some rifles bump-fire but have recently run into an M305 that would double very reliably. This last was likely a problem with the disconnector.

 

[Keithjohn]

Keithjohn - If your M305 is double firing make sure that you don't have a defective trigger. I've seen some rifles bump-fire but have recently run into an M305 that would double very reliably. This last was likely a problem with the disconnector.

Thanks , I was wondering for awhile but mine is a S.A. National match and I think the lack of clearance along with the soft primers was the main culprit (I hope and knock on wood ) it hasn't happened since I have started taking all precautions (only a few hundred rounds ) so I'm hoping the trigger is ruled out but if it happens again with the regularity that it was I will be taking it for a checkup

 

[stevebc]

Ok, turning off the gas is something I hadn't thought of. I did say I'm new to this, lol.

I'll keep at it, thanks for the suggestions.

 

[bigedp51]

I may have got this wrong, but here's what I've done:

I took an unsized fired case, tapped out the primer, and re-inserted it quite proud.

Chambered it by inserting brass in chamber and:
- letting the bolt slam home on it,
- easing the bolt home, then pushing firmly on the op rod until it fully closes.

Either way, the difference I measured was .004

So do I set the die to this fired length brass, then take it down .003 to .004?

Other stuff: I'm using standard RCBS .308 Win dies and my M305 is chambered in .308 Win, not 7.62 x 51, if that helps.

Should I just go ahead and buy some small base dies?

When you check the case after shutting off the gas port again use a "resized case" and the primer method for checking your head clearance.

The resized case should have the primer protruding .003 to .006, meaning the case will be this much shorter than the chamber.

Also remember the spring back rate of different brands of brass will vary and the shoulder location after resizing can also vary.

On a semi-auto the bolt has enough weight when it slams home to shorten the case from inertia so let the bolt close "slowly" to get a more accurate reading.

I use my Hornady case gauge to adjust the die for proper shoulder bump and a JP Enterprises Case Gauge for a final plop test to check the loaded ammo.

The JP Enterprises Case Gauge is cut with a chamber finish reamer and also checks case diameter. The other type case gauges only check the length of the case.