copied and pasted from airgunbbs>firearms>HMR throat erosion, posted by "some bloke"
Date: 16-4-2012. Time: 0830hrs
HMR throat erosion?
I've shot some 8000~9000 rounds through my Sako Quad hmr barrel and it occasionally goes off song but clears up again after a darn good shafting with Tetra gun copper solvent/amonia and Bench rest copper solvent. Of late it has taken longer to settle down again after a good rodding but it gets there in the end.
All was well until I ran out of Hornady HMR rounds, my local RFD had none in stock. I went with his recomendation of some Winchester rounds on the understanding that he would change them if the gun no likey. I went to zero them at 50 yards as a starter. Well first magazine full and they didn't load smoothly: The necks arn't crimped and the proud edge fouled the breech as the bolt pushed them forwards.
First shot there was a very unusual report, I checked the bullet had left the barrel ok. Next few rounds were all over the place I gave up trying groups of three and went for five instead. Typical group was one sounded bad, and the others grouped about 6", sometimes missing the A4 sheet. I gave up after 40 shots. I've given the barrel the most intense shafting ever and it's still all over the place.
I tried zeroing again this morning, first with some Remingtons that I was given, no success and then some Hornady's that I managed to source last week. At one point I got some touching at 50 yards but on the whole still flying all over the place. I again gave it a ruddy good seeing to this morning with a new nylon and new bronze brush and became aware that the cleaning rod doen't start to twist untill the brush is something like three to five inches up the barrel. Is that normal?
The crown looks perfect even with a magnifying glass and in desperation I have cleaned out and put new baffles into the Utra mod.
The rifle was supplied as a .22. The HMR barrel is listed separately so if i want to change it I'll have to go through the variation rigmarol.
Thoughts and ideas please gents.
--------------------------------------------------------------------
The key response is this:
----------------------------------------------------------------------
Sir, in talking to friends over the water, this time last year on reading a similar tale of woe on another site, I find that your SAKO quad barrel has lasted about three times longer than any of theirs.
Be grateful.
A squint into the area of the leade of any of their barrels shows strong speckling/frosting and a marked reduction in accuracy in around 3000 rounds or so. A pal of mine in Eugene OR shot out his barrel in under 2000 rounds - from 3/4" ten shot groups to 3-4" groups - he is no mean shooter, being the county BR champion as well. The lack of rotation on your cleaning rod shows that your rifling has been 'burned out' in this vital area, and no amount of cleaning will replace it.
In a word, your barrel is now a a hose.
IMO writing a snottogram to SAKO will do you little good, as a round-count like yours would be considered far above average, but you could try it and let us know how you get on - there are more than a few such rifle combos in my club.
tac
Edit - a couple of points re your habit of shooting consecutive groups. - IMO you are treating this hyper-velocity rimfire like a competition target rifle, something it is decidedly not. It was intended to be used in a less frantic manner, and I have to ask if you'd shoot any centre-fire hunting cartridge the same way? Throat erosion of the type you've got only takes place when the constant firing of groups does not permit the gun to cool down sufficiently - this is why many of the higher-calibre target rifle shooters change out their barrels for every season of shooting. Some, like the 6.5-284, burn out in less than 1500 shots and are useless thereafter except as expensive rebar for laying concrete flooring. You seem to have joined the same group of shooters, but after an extraordinarily long life for your barrel. Like I said, be grateful.