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Posted: 7/10/2004 4:52:04 PM EDT
| After I wore the throat out in my Douglas barrel I replaced it with an Olympic Arms SS Ultra match 1x8. The accuracy was never as good as my Douglas but it was acceptable. I have had it about a year with about 2000 rds. thru it. Lately the accuracy has opened up to 2 1/2 to 3 inch groups with ammo that normally gives 1 moa. While cleaning it, it appears that there is a loose spot in the barrel about 4 inches before the gas port hole. The cleaning rod has no tension each time it comes to this area and then has tension again. I have not pulled off the float tube to mike the outside of the barrel yet but I suspect it is bulged. What happened? Improper heat treatment? dirt in the barrel when firing a round? Manufacturing defect? Is this normal? |
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A couple of points, The first is that in general, a Cut broached barrel will fall off/take a dive before a button rifled barrel. On a cut barrel, you can expect between 2000-2500 rounds before the groups starts to open up rapidly. On the button rifled barrel, the groups tend to open up around the 2000 mark, but do it more gradually until you just get to the point that you consider the barrel gone (maybe 5000 unless you a capable of tack driving). But the rub is that the cut broached bore will group better than the button bore due to the barrel tension (the way that the rifling is produced). So with this in mind, you have to dig past just the barrel blank (match bore blanks) and look into the total process of the completed barrel. You have stated two different types of barrel blanks, and may have overlooked the most importation part, the production of the barrel. In regards to the Douglas barrel, great care was taken to chamber the match blank in regards to work with a target type load (longer ogive), and then the barrel was hand lapped to further unify the rifling. On the Sum barrel, since it is a production barrel, it is reamed to a semi 223-match chamber (shorter throat, but still a tad wide in the side walls), and never really hand lapped to the point of truly trying to unify the lands. The Sum barrel is a great production barrel, but not a true sampling of a custom Broached cut barrel blank produced by any of the barrel maker on the market. Hell, to just point it out, you can’t even buy a match broach barrel blank for under $300, much less get a Krieger/MAC final produced one for under $450. Was the barrel really defective from the start? The fact that the barrel had some variances in the rifling from the start (more than if it was a true match blank), no lapping was done to try and minimize them, and the bullets deforming as it traveled down the bore just did it in. My guess is that right before the section that you are referring to, the lands went narrow, and the groves went deep. As the engagement of the bullet lost the continuity of the rifling (bullet lost engagement contact), when it hit the tighter section, it caused excessive wear to that section (worn section may have been normal, but the section right before was oversized). The 2000 bullets moving down a non-unified bore, and the deformities that occurred to the bullet just wore the rifling out at the given point. Granted that you may have bulged the barrel, but my guess it that the lack of unify of the rifling was the key factor to its demise. Now comes the tricky part, Will Oly replace the barrel as a defective barrel? Only they can answer that question, but you did manage to get 2000 rounds threw the cut rifling bore, so basically, the barrel was at the point to give up the ghost anyway. Should you go back to a custom barrel over a production barrel? Only you can answer that question, but remember if you do go back to a Sum barrel, it’s a Production barrel. This means that you will need to spend the time hand lapping the rifling to try and unify it (as much as possible from a non match barrel blank), and need to tailor your reloads around the non-true match type chamber to get the most out of the barrel. If your skills have surpassed the capabilities of a production barrel (even the SUM) then you need to step back up to a custom barrel. Also, since you stated that your around 2000 rounds a year out of this rig, You really need to decide on what type of rifling produced barrel you are going to run. The Broached cut barrel may get you threw a year (starting with a new barrel as the season starts and praying to gods towards the end of the season), or you could run a button cut barrel and get twice the mileage out of it (still keep you in the hunt to the 5000 mark). Most shooters know the limitation of the broach cut bores, and even though they will produce better groups on the whole (match blanks), the fact that the barrel will just give up the ghost with out warning at such a short period (2000-2500 mark), makes the rifled cut barrels a better option for a lot of them. So to sum it up and answer your question, if you don’t find an outer bulge caused by foreign matter in the bore during firing, yes you wore out the barrel. |
| Thanks Dano523, I pulled the float tube off of it today and miked the barrel. It varied by .002 all the way down the barrel so it is hard to tell if I bulged it. It would appear that I wore it out. I had a Glock 9 mm barrel that did the same thing. Glock replaced it free of charge. As far as decisions on what to replace it with I will have to give that some thought. A lot has been written on this forum about barrels so I will have to do more research. It could be time for a dedicated 22 upper for a lot of my practice to save wear and tear on the new tube. Thanks again for the reply. |
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For Douglas/Krieger barrels. www.compasslake.com/ www.compasslake.com/Price%20List.htm For Mac barrels, www.gunsport.net/chanlynn/ Note: Mark produces his barrels in caliber groups. You may have to wait over a year to get a barrel. |
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