Marlin Firearms Forum banner

1 - 20 of 54 Posts
Joined
·
1,875 Posts
Discussion Starter #1
We generally don’t get more than a trickle of 308 Marlin Express rifles through the shop, but we’ve seen enough of them now to get a close look at the gremlin that haunts them. As many of you know, the 308 platform has been dogged by frequent reports of sticky lever issues and high pressure signs. With a max chamber pressure around 47kpsi, this simply shouldn’t be happening.

Several months back a customer sent us several MXLRs for work, among them a pair of 308s. These were purchased off Gunbroker and shipped to us directly, so our customer was unaware of any issues, but part of our job was to evaluate them before doing any custom work. One of the .308s shot fine, but the other had a stuck lever on the first shot, followed immediately by a dangerous case separation on the second. Always an exiting event.
A couple of quick measurements revealed the problem: the bad rifle had .014” head space on Hornady’s factory ammunition. Since Leverevolution is pretty much the only game in town for 308 ME, we decided the best course of action was to adjust the head space of the rifle to match the ammo. All issues disappeared promptly, and the rifle shot beautifully on its next range test.

More recently, JackTW called me to discuss an apparent head space issue with his 308MX. After several conversations we began to piece together what was going on in the sample of rifles we were able to evaluate. It is a highly unusual problem, compounded by more than one error.

The first problem is that both Jack’s and my sampling of LVR ammo was drastically undersized from SAAMI specs, to the tune of nearly .020”. The second problem was that Jack’s resizing die, if touching the shell holder, more or less replicated this gross under sizing. The third issue as that a small sample of rifle chambers revealed that they too were undersized, but unfortunately not nearly enough to compensate for the drastically undersized ammo/brass. The difference still yielded actual head space in the .010-.014” range.

For those of you not well versed in proper head space etiquette, the simplest way to think of it is the gap between the bolt face and the case head, when the cartridge is fully seated in the chamber. A gap of .000-.002” is highly desirable in precision bolt actions, though typically only achieved with hand loads. A gap of .003-.006” is pretty optimal for sporting and defensive arms, as it helps ensure reliable chambering under less than ideal conditions. Ammo makers generally size their brass a few thousandths of an inch under the SAAMI minimum spec chamber for reliability’s sake. A gap of .007-.010” is detrimental to accuracy and brass life, but generally not unsafe with good brass.

Once head space gets into the .007-.010” range it’s not unusual for misleading pressure signs like flattened primers to occur. In the case of lever guns, sticky levers may also hint falsely at excessive pressure. Gaps larger than .010” transition into dangerous territory, and once into the teens the likelihood of a ruptured case gets very high.

There is a quick and dirty way to measure head space with your ammo. In the situation with the 308ME this is necessary, because at least in some cases neither the chamber nor the ammo is at SAAMI spec, so a head space gauge won’t help. You can use masking tape as a cheap feeler gauge. Cover the case head with masking (painter’s) tape, trim the excess tape, and check the fit in your chamber. DO NOT FORGET TO ENGAGE THE SAFETY FIRST. Most masking tape is about .003-.004” thick. If your lever will not quite close on the taped case head, then you have an unusually snug factory chamber, but you’re in good shape. If the lever will just close on one piece of tape, but not two layers of tape, you’re in the optimal zone. If the action will shut on two layers of tape, but not three, you’re a little loose but probably safe. If three layers of tape still don’t prevent the lever from closing all the way, you have dangerously excessive head space, at least with that ammo. In any event, it’s a good idea to mic the tape just to verify its thickness, and remember that tape can compress slightly under pressure.

If your rifle has—or you strongly suspect it has—excessive head space, there are two possible cures. The first, if you’re lucky, is that a new locking lug may be fitted to close up the head space gap by several thousandths. If you’re not so lucky, your rifle may already contain a thicker lug (they are bevel cut in different thicknesses at the factory) and fitting a new lug won’t improve matters appreciably. Failing option 1, the only remedy is option 2: setting back the barrel by one thread turn.
Fitting a new locking lug usually takes a couple of hours to do well. Setting back the barrel gets pricey, as the breech features must be recut, and the forend and mag tube must be refitted to their new hanger locations.

There is a third option. It’s less a remedy and more a work around: fire form all brass in your chamber, and then pay careful attention to head space when resizing. If your rifle has in excess of .010” HS I don’t recommend fire forming with factory loaded ammo. Even if a case separation doesn’t occur on the first firing, the brass may have stretched enough to cause premature failure. Far better to use the tried and true method of fresh brass, light powder charges, and bullets seated snugly in the lands.
Hopefully this will help alleviate some of the frustration associated with the otherwise superb .308 Marlin Express cartridge. It’s a real shame that this rifle/cartridge combo has been plagued by a seeming lack of regard for published SAAMI specs. But if we Marlin lovers stick together on this, perhaps we can get things sorted out or own way. As always, we at RPP are here to help.

Best wishes from the hurricane zone,

AD
 

·
Premium Member
Joined
·
11,276 Posts
Thanks Adam, I suspect those with 338MX's that have the same issues have identical problems.

Stay safe with this weather Adam and family.
 

·
Administrator
Joined
·
27,727 Posts
Adam, I appreciate you taking the time to explain this issue.

Folks, Adam and I have been discussing this issue for some time as my 2007 308MX chamber is under SAAMI Specs making it too tight. I'm currently out of pocket and on my phone. I will be posting some data once I get home.

As most know, I've developed bullets specifically for the 308ME and quickly realized the issues. Jay, Ret_Eng, has been helping with developing load data and various shooting tests for me with his 308MX. Our rifle chambers happen to be a carbon copy. Jay has been a big help to my R&D as well as Adam has been with this chamber issue.

The data I'll be posting will especially help those who roll your own.

Jack
 

·
Super Moderator
Joined
·
24,763 Posts
Adam, I appreciate you taking the time to explain this issue.

Folks, Adam and I have been discussing this issue for some time as my 2007 308MX chamber is under SAAMI Specs making it too tight. I'm currently out of pocket and on my phone. I will be posting some data once I get home.

As most know, I've developed bullets specifically for the 308ME and quickly realized the issues. Jay, Ret_Eng, has been helping with developing load data and various shooting tests for me with his 308MX. Our rifle chambers happen to be a carbon copy. Jay has been a big help to my R&D as well as Adam has been with this chamber issue.

The data I'll be posting will especially help those who roll your own.

Jack
---and Jack and I did the fire form brass method plus use the Hornady head space comparator tool to figure out what the actual head space gap was in our rifles. Once we got that issue figured out--the accuracy of my rifle when testing Jack's 308 ME bullets improved dramatically. I also believe Grumpy Bear's statement about the 338 ME rifles to be true as well. I am beginning to believe my 338MX reloaded brass case life is cut short due to the tight chamber issue.
 
Joined
·
1,875 Posts
Discussion Starter #6
I'm still not entirely sure that the 338s have a similar issue. I just haven't seen a large enough sample. The .338mx I have now exhibits perfect HS (about .004") on Hornady ammo, has a good looking chamber, and the lever is very slightly sticky after firing. It's a good rifle that shoots well under MOA, but it doesn't tell me much.

What I can say with a fair amount of certainty, thanks to a lot of experimenting, is that lever guns are generally more sensitive to HS than bolts and semi autos. With a lever gun you will often get definite signals when something is out of wack in the chamber, and this seems to be particularly true of cartridges that head space on the shoulder rather than the rim. 20th century chamber pressures amplify these signals, even though they may be perfectly safe in the rifle.

In addition to indicators like flattened primers and sticky lever opening, another is the lever popping open on firing. This latter can indicate an overly tight HS, as in near zero or even less, and does not necessarily indicate excessive chamber pressure. The trick is figuring out what the signs mean. The indicators can wear more than one hat.

Chalk up one more benefit to loving lever guns: they give you a heck of an education on internal ballistics if you pay attention.
 

·
Administrator
Joined
·
27,727 Posts
Just arrived home so let's see if I can convey this data reasonably well enough :alberteinstein: for all to make sense of it.

First, according to SAAMI the proper HS for the 308ME is 1.5377 min to 1.5477 max.

Hornady's factory ammunition measure 1.5270 case head space, determined using Hornady's Headspace Comparator Kit. To the SAAMI minimum HS of 1.5377, the difference is 0.0107. Not all that good when you consider this is to SAAMI's minimum HS data. What about folks with 308ME's whose HS measures between to max HS? Well, we've heard of folks complaining of sticky extraction to their rifle won't print anything less than 5 or 6 inch groups. With Hornady's factory ammunition being case HS where it is it doesn't surprise me.

I fully fire formed some cases in my 308MX, IOW, to the point when I chamber my fired cases the lever will not lock up. This is fully fire formed. Using Hornady's HS Comparator they measure 1.5335. SAAMI min HS of 1.5377 - 1.5335 = 0.0042 below minimum SAAMI minimum HS spec, IOW, my rifles chamber is a tad tight!
My fire formed case at 1.5335 - factory ammo of 1.5270 = 0.0065 which is within Adams mention of being optimal for sporting and defensive arms. Yet, remember, my chamber is below SAAMI min HS spec and some folks 308ME chambers can be mid to max SAAMI HS spec.

So, a SAAMI max HS chamber of 1.5477 - Hornady factory ammo of 1.5270 = 0.0207! Ouch, rifles at SAAMI max HS are not goinng to perform well. Considering a midway SAAMI HS of 1.5427 - 1.5270 = 0.0157 which is unacceptable.

Now, to compound the HS issue (Gremlin), Hornady's NEW factory brass measures a consistent 1.5225 which is an additional 0.0015 thousandths shorter HS than factory ammo. Therefore, in my too tight chamber of 1.5335 - Hornady's new case HS measuring 1.5255 = 0.008. Firing factory ammunition in my too tight chamber I get case stretch measuring 0.0085. That is too much case stretch for brass longevity. Not to mention, loads readily demonstrate high pressure signs.

Worse, my Hornady dies full length sizes cases measuring 1.5160 - to my chamber measuring 1.5335 = 0.0195 difference. Utterly unacceptable! Folks, not all Hornady 308ME dies under size cases when full length sizing as I have asked other folks to measure what they're getting but since mine do, I highly recommend checking your dies.

Obviously, I bump size (HS size) my cases rather than full length size them. I shared all this with Jay, Ret_Eng, and we both now bump size or HS size cases to .004 HS. To measure your 308ME chamber, you need to fully fire form your cases, then measure them using Hornady's HS Comparator Kit. The kit is not expensive and is worth every cent if you're loading your own or you're rifle is experiencing sticky extraction or poor groups, get one! You'll get brass longevity, remedy high pressure spikes as well as improving your loads accuracy.

I also have gone to precision case prep loading for my 308ME and the results are very impressive. I'm wrapping up my load data and getting ready to launch my bullets. I know, it has taken a good amount time longer than I expected and it's due to figuring out the above issues. When I debut my bullets for this cartridge, all of this will be discussed so as to properly hand load for your specific 308ME chamber.

I hope this helps some folks understand what is going on with their 308ME and help remedy their situation. Many thanks to Adam of RPP, your help with what you've found with customers 308ME's was most useful.

Folks, if you're having sticky extraction issues or poor groups, you can figure out why and Adam is the go-to expert to remedy it.

Hope this is helpful and I welcome questions.

Jack
 

·
Administrator
Joined
·
27,727 Posts
Adam, once this thread runs it's course, I'll make it a sticky. :top:

Jack
 

·
Super Moderator
Joined
·
24,763 Posts
Jack used the term precision prep of brass, that means uniforming the brass case flash hole and primer pocket. It helped out my 308MX accuracy and case life of my brass. The tools to perform these case prep functions don't cost a lot and I highly recommend using them. One other thing I might add--is the Remington 308 ME factory ammo that I bought a few years back measures out much shorter with my HS gauge compared to my chamber (which in itself is tight)--just like the Hornady factory ammo did as Jack stated. My Remlin 308MX HS measured out as 1.536 inches with my Hornady comparator but the Remington factory ammo miked out at 1.527 inches--which ain't good. I wasn't too thrilled at trying to fire form that ammo in my rifle. I had to fire form my empty brass using a handloading recipe that I developed for my rifle 2 years ago using a 170 gr Sierra Prohunter bullet (30-30 FN bullet) and bumping up my LVR charge a little bit.
 

·
Administrator
Joined
·
27,727 Posts
I never thought I'd need to incorporate precision case prep, consisting of uniforming primer pocket and flash hole, for a lever cartridge but they are a high performance round. Yet, I began doing so to help mitigate pressure spikes due to the short brass to HS, that even in my too tight chamber. This along with HS sizing my cases at .004 HS, and seating bullets to lessen the jump to lands, has proven to resolve any high pressure signs and greatly improved accuracy. I passed this onto Jay who did the same with identical results.

This will all be detailed when I debut my bullets as well as sharing some loads that deliver some truly impressive velocity gains.

Jack
 

·
Registered
Joined
·
5,590 Posts
I never thought I'd need to incorporate precision case prep, consisting of uniforming primer pocket and flash hole, for a lever cartridge. Yet, I began doing so to help mitigate pressure spikes due to the short brass to HS, that even in my too tight chamber. This along with HS sizing my cases at .004 HS, and seating bullets to lessen the jump to lands, has proven to resolve any high pressure signs and greatly improved accuracy. I passed this onto Jay who did the same with identical results.

This will all be detailed when I debut my bullets as well as sharing some loads that deliver some truly impressive velocity gains.

Jack
Got a better idea when your release is?
 

·
Administrator
Joined
·
27,727 Posts
Got a better idea when your release is?
Well, I have very little to finish up but the searing triple digit heat isn't helping. Hottest summer I can recall and July was the hottest on record, August is nearly as bad. I was set to shoot this weekend but the temps climbed to 102 cancelling the shoot. Hell, I'd welcome lower 90's!

That said, I'm going all out to launch in September.

Jack
 

·
Registered
Joined
·
5,590 Posts
Well, I have very little to finish up but the searing triple digit heat isn't helping. Hottest summer I can recall and July was the hottest on record, August is nearly as bad. I was set to shoot this weekend but the temps climbed to 102 cancelling the shoot. Hell, I'd welcome lower 90's!

That said, I'm going all out to launch in September.

Jack
Woo-hoo!
 

·
Super Moderator
Joined
·
24,763 Posts
Well, I have very little to finish up but the searing triple digit heat isn't helping. Hottest summer I can recall and July was the hottest on record, August is nearly as bad. I was set to shoot this weekend but the temps climbed to 102 cancelling the shoot. Hell, I'd welcome lower 90's!

That said, I'm going all out to launch in September.

Jack
JACKTWs bullets will also work in the 300 Savage/308 Win/30-06--etc. I am working up a load for my old '57 99F 300 Savage since my 308MX Remlin is in the shop for repair. My 1952 Remington Model 721 30-06 loves them as well. I just need to re-zero my old Weaver V8 scope and I will have a hunting load to use this coming fall.
 

·
Administrator
Joined
·
27,727 Posts
Pics of the new bullets please!
Saving the pics until the debut, Goose. I promise, the wait will be worth it and you won't be disappointed.

Jack
 

·
Registered
Joined
·
9,157 Posts
Hey Jack, it's September!:D DP
 

·
Administrator
Joined
·
27,727 Posts
Yeah, but, but, September has 30 days! :biggrin:

I do hope to launch ASAP.

Jack
 

·
Super Moderator
Joined
·
24,763 Posts
Hey Jack---You said Sept but not the year! :D
 
  • Like
Reactions: dpe.ahoy and JACKTW
1 - 20 of 54 Posts
Top