trodrig Posted October 8, 2007 Share Posted October 8, 2007 In developing loads for my STI Trubore I've been looking at the primers and watching for pressure signs. I'm not seeing any pressure signs yet (just now getting up to major PF and taking it real slow) but I am seeing that the firing pin strikes are no where near centered on the primer. Is this indicative of a problem with my loads or possibly the gun/extractor? All rounds drop in/out of the chamber with no problem. I'm loading 115 grain Montana Golds at 1.240" OAL. Gun has an Aftec extractor. Using brand new Starline Super Comp brass and Winchester Small Rifle primers. Thanks, Trodrig Link to comment Share on other sites More sharing options...
al503 Posted October 8, 2007 Share Posted October 8, 2007 If you're shooting supercomp, then it's absolutely normal. If you're running rimmed super, then I'd be scratching my head also. Link to comment Share on other sites More sharing options...
XRe Posted October 8, 2007 Share Posted October 8, 2007 You're good, dude. Its basically the difference between the rim sizes in .38 Super to Supercomp that does it.... Link to comment Share on other sites More sharing options...
trodrig Posted October 8, 2007 Author Share Posted October 8, 2007 Cool! Thanks guys! Trodrig Link to comment Share on other sites More sharing options...
Joe4d Posted October 8, 2007 Share Posted October 8, 2007 What ????????//,,,, I dont get it, not argueing as I have no first hand experience with either round, but what does the rim have to do with it ? The round goes in the chamber, the primer is center of the brass and the brass should be centered in the chamber, The firing pin should be centered as well, how does different rim size have anything to do with that ? Link to comment Share on other sites More sharing options...
Flatland Shooter Posted October 8, 2007 Share Posted October 8, 2007 What ????????//,,,, I dont get it, not argueing as I have no first hand experience with either round, but what does the rim have to do with it ? The round goes in the chamber, the primer is center of the brass and the brass should be centered in the chamber, The firing pin should be centered as well, how does different rim size have anything to do with that ? Joe, I'm glad you asked. They got me scratching my head over this one. Bill (Or did Dave open an April Fool's thread early?) Link to comment Share on other sites More sharing options...
al503 Posted October 8, 2007 Share Posted October 8, 2007 I believe the breechface on STI's were designed for rimmed 38 super or 9mm. I guess there isn't enough of a difference to between those and the SC to require a change to the breechface specs. Link to comment Share on other sites More sharing options...
XRe Posted October 8, 2007 Share Posted October 8, 2007 how does different rim size have anything to do with that ? Because, for whatever reason, it alters how the round tends to sit in relation to the barrel and breechface. One of the resident gunsmiths can probably explain the mechanics better than I can. Any of the Supers will apparently tend to be slightly off center anyhow, depending on the specs of the parts - but the rimless Super variants tend to be more off-center when fired in the same gun. Link to comment Share on other sites More sharing options...
HI5-O Posted October 8, 2007 Share Posted October 8, 2007 I thought it had to do with how a barrel is fitted (how high/low) in the locking lugs of the slide. barry Link to comment Share on other sites More sharing options...
HSMITH Posted October 8, 2007 Share Posted October 8, 2007 As long as it is somewhat centered it will be fine. There are a lot of factors in play here, among them lug engagement, firing pin tunnel location, breechface rail position and width, and probably something else I have forgotten about. It isn't uncommon, and isn't necessarily a 'bad' thing. Throw up some pictures of the brass with a mark to indicate where the extractor is. Link to comment Share on other sites More sharing options...
mcattack Posted October 8, 2007 Share Posted October 8, 2007 A few things can cause that situation and it can cause problems if the main spring gets weak. If it is off center enough you can get miss fires. Extractor can push the case a very small amount but if the chamber is tight then the extractor is not the problem. More than likely it is the lock up of the slide barrel and lugs. The firing pin should be very close to center if the barrel has been fit correctly. Link to comment Share on other sites More sharing options...
trodrig Posted October 9, 2007 Author Share Posted October 9, 2007 Here's a picture of brass from three different loads. I don't know how they were sitting in the chamber when fired so I'm not sure where the extractor was located. I can keep track of that next time if ya'll think this is bad enough to be concerned with. These were three different loads. From left to right they are 7.5gr SR7625, 7.5gr Longshot, and 9.1gr SR4756. Only the 4756 load is making major (~166PF). The other two are close but not quite there. Do any of these primers look too flattened to you guys? I didn't think they looked that bad and was planning on stepping up both the SR7625 and Longshot loads by another couple tenths of a grain. Thanks! Trodrig Link to comment Share on other sites More sharing options...
Kingman Posted October 9, 2007 Share Posted October 9, 2007 I was about 8.1 on longshot or so I think. Link to comment Share on other sites More sharing options...
HSMITH Posted October 9, 2007 Share Posted October 9, 2007 The far left one is showing some pressure, but doesn't look too exciting. Look in the extractor groove, you will see a mark or a shiny spot where the extractor pulled the case from the rim. You will also see a dent in the headstamp where the ejector knocked the case out of the gun. Line up the extractor marks at 3 o'clock and shoot the picture again. Barrel fit is only ONE variable that affects firing pin hits. High or low or left or right doesn't necessarily mean the barrel is poorly fit. Link to comment Share on other sites More sharing options...
trodrig Posted October 9, 2007 Author Share Posted October 9, 2007 Well, the extractor mark was very subtle but I think I found it and lined all of them up at 3 o'clock in this new picture. Looks like the primer strikes are all off to the right a little. Thanks! Trodrig Link to comment Share on other sites More sharing options...
HSMITH Posted October 9, 2007 Share Posted October 9, 2007 Pretty normal for SuperComp on a Super breechface to have them off to the right a hair. Yours are a little further off than what I would expect to see but no where near a problem in my opinion. Hits are good and hard, centered enough to get plenty of anvil in the primer too. Between drill walk in the firing pin tunnel drilling, SuperComp on a Super slide, and normal manufacturing tolerances you will see things like this. I wouldn't worry about it, if the gun runs keep going. Link to comment Share on other sites More sharing options...
trodrig Posted October 9, 2007 Author Share Posted October 9, 2007 Thanks HSMITH! So far the gun's been running good. I've only put 200 rounds through it over the chronograph working up to major, but, so far so good! Thanks everyone for taking a look! Trodrig Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now