How much throat erosion during run-in. 6.5x47 ?

[Guest richness]

Chaps, after good result initially with my 6.5x47, things went bad recently. ALL loads I was powder testing slipped right away.

Long story short, as i've covered the load development in a separate thread, the seating was in a sweet spot of a few thou - it certainly couldn't get much shorter before falling off. So i got my OAL guage back off my mate to see if the throat had bedded in a bit over the first 400 shots from when I measured it when new. This would mean, clearly, that i need to space my rounds out a little to compensate and would explain the drop in accuracy.

Well i measured once with my oal guage and then it snapped SO miffed about that but anyway the result was 17thou longer than originally (2.181 vs 2.164)

Do you think this is a wrong result? OR is that a reasonable amount of erosion from new as the lands bed in? I imagine that it would now start to steady down? My 243 win ran hot and ended up eroding about 1thou per hundred shots....so this seems a lot (but i didn't check when new/bedding in)? Barrel is a Trueflite 1/8 f-class contour 29". Load has been 2960fps RL15 37.6gr CCI 450 7thou IN

Any experience shared would be very useful as i now have no oal guage and i'm not delighted about the delay while I get one in from midway at a a cost of £40 and all the while pulling my hair out about this....

Many thanks, Richard Utting

 

PS the latter pages of this thread show the development of the load: http://ukvarminting.com/forums/index.php?showtopic=9203

[6mmBR]

You may find its not all throat erosion.

Your differiing OAL may be artributed to different lots of bullets and variations in thee ogive.

My 6x47 had only altered 5 thou in 1200 rounds.

You would need to use the same bullet to get a consistent variation of throat errosion.

I kept the origional bullet Neil used to set up the seating depth for future refference.

Cheers

Dave

[Guest richness]

Thanks yes this bullet was indeed from different batch, with ogive to base measurement 5 thou different, but that doesn't affect oal guage readings by 17 thou....

[onehole]

I have studied throat erosion a lot with my rifles and have been very careful to get exact measurements of what is really going on.What I have found that initial bedding in and perhaps a 100/200 round count will generally wear away about 5 to 10 thou maximium.Just running in say over 10 to 30 rounds only 5 thou.

Main errors in measurments come from using different batches of heads and badly fitting dummy cases etc.The only way with a "Stoney point" method is to use a once fired case that truly fits the chamber and just threading out the fired case and inserting that can sometimes be too tight a fit and can give "long" readings.You have to fit the fired case to the chamber and sometimes this needs a little fettling with some 1200 grit emery until you get a really snug fit that repeats every time.

Your 17 thou is probably a combination of red herrings and not throat erosion to that extent I,m sure,pM me if you want to know a bit more about using dummy cases etc.Regds Onehole.

[Guest richness]

I have studied throat erosion a lot with my rifles and have been very careful to get exact measurements of what is really going on.What I have found that initial bedding in and perhaps a 100/200 round count will generally wear away about 5 to 10 thou maximium.Just running in say over 10 to 30 rounds only 5 thou.

Main errors in measurments come from using different batches of heads and badly fitting dummy cases etc.The only way with a "Stoney point" method is to use a once fired case that truly fits the chamber and just threading out the fired case and inserting that can sometimes be too tight a fit and can give "long" readings.You have to fit the fired case to the chamber and sometimes this needs a little fettling with some 1200 grit emery until you get a really snug fit that repeats every time.

Your 17 thou is probably a combination of red herrings and not throat erosion to that extent I,m sure,pM me if you want to know a bit more about using dummy cases etc.Regds Onehole.

 

Excellent info thank you

I will take you up on that later for sure, thanks.

For now, i'm going back to empirical testing to get the rifle back on point: I'm making my loads up 19thou longer, going to the range with the hand press and testing them from long to short until they come together.

Interesting read mind; i had imagined that it would be reasonable for the edges of the rifling to wear more rapidly during initial use, then settle down thereafter. In future, i shall pay particular attention to maintaining my jump to the lands during and after run-in.

[brown dog]

PM me if you want to know a bit more about using dummy cases etc.Regds Onehole.

 

A photo-rich thread explaining your method would be interesting to many of us; if you'd be happy to write it

[foxing2night]

Hi Rich,

I have to agree with 6br and one hole,,,,

 

Dont get to hung up on this subject??, As trying to get consistent measurements can drive you bloody

mad!!!!

 

If you are in doubt load one round long, gently chamber and then take it out,,,

you should now be able to see the rifling marks on the bullet??, measure the length of the marks,

take this away from the length and you will have the measurement of a loaded round that will just kiss

the rifling of your rifle,,,,

 

Loads of ways to achieve the same result,,

 

On all of my rifles i do not load into the rifling???, only just to kiss it!!!!!

 

I will take some measurement off mine this week and get back to you,,

 

Darrel

[Guest richness]

Well I loaded up some rounds 18thou longer. Which if the new measurement to the lands was about correct,which i feel it was, would put me 8thou into the lands, about where I wanted to be, going from previous results.

Well i tested from that length down, getting shorter every batch.

The new longer rounds felt immediately more like it WRT chambering feel

Results were that the longer ones (8thou in with the new measurements) were the best, doing a little over 1" @ 300y

Every 2thou shorter gave worse results

I shall make up another batch a couple of thou longer, putting me 10 or 11thou into the lands.

My conclusion is that the throat has indeed moved back about 18 thou from new.

I'll fine tune for the seating sweet spot tomorrow but all things being equal I will have gone from 2.172 to 2.192 give or take a thou.

I'm not necessarily bothered about accurately measuring to the lands...what i'm obviously bothered about is chasing the lands precisely as they wear so that i can keep my seating in the sweet spot. Through trial and error, I ended up lengthening my 243 load (bartlein 1/8 27" 105amax rl19 43,7gr) 1thou per hundred shots after i got it settled in on that load which was not from new but from about 700shots old.

Warmest regards to all, Richard

[onehole]

A photo-rich thread explaining your method would be interesting to many of us; if you'd be happy to write it

Not exactly photo rich but a little more on the subject:If one is using the "stony point" type method you can easily come unstuck and have some false readings thats why I made my own rod assembly that clamps a rod inside a rod but does not cause any indentations on the inner rod over time.Coupled with this and always using a once fired threaded and fitted case I can make spot on jam figures and chase wear and reassess new batches of heads accurately. The threaded once fired case can be too tight a fit in the chamber and with the help of a small lathe and some 1200 grit it is easy to remove a little brass[under a thou!} along the case to make sure that case snugs completely into your chamber and without any force.

The difference between using a "modified case" and a once fired case is quite a lot and enough to get you either too close or well into the lands in error!!!Below are some pics showing some mesurements of my 6BR cases and you can see that a "7" thou difference exists on "Jam" figures and I have proven this by making up "dummy" rounds to identify land markings.The other measurements are at the shoulders and case head diameters.

Now when I load my 105 Amax at 1.760[OG] they really are 10 thou off!!! and not 3 thou!!! This is only one example and I have seen the opposite of this occur in other calibres/rifles as well!!!!

To close I would also recommend the split or slotted neck method but someone else can explain that one,cheers take care,Onehole

[baldie]

I,m just about to start and make a minature Stoney style gauge for a customer of mine, who i built a .17 Ackley hornet for. The hornet case is too small for the stoney point gauge, so i,ve sourced some bits for a copy.

Chester, get your arse in gear and send me a fired case this time The guage wont cost you a bean.

[Laurie]

Dave,

 

there is an alternative to the Stoney-Point gauge - the Sinclair Seating Depth Gauge that is a rod and collars system. Unlike most home-brewed rod systems that work from the muzzle, this is inserted from the rear of the action firstly against the base of a bullet dropped into the leade through a cleaning rod guide, then against the head of a fireformed cartridge case pushed fully into the chamber. Sinclair claims it is ineherently more accurate than the Stoney-Point (the issue already noted about modified case-chamber fit).

 

You could knock one up a lot quicker than a downsized Stoney-point I reckon using a smaller diameter rod if needed. Another alternative is necking down a Hornady / Stoney-Point .22 Hornet modified case which comes atop an adapter so it fits the larger diameter tool body. I have one you can have cheap if you're interested as I don't see me ever loading .22H again.

 

I'll ring you re the Rem 700SPS Tactical project shortly and can bring them along to yours. (Also, found a load of cast lead .30 Carbine bullets, some gas-checked, and some Sierra 110gn jacketed RNs the other day - still haven't found the Viht N105 I tried in the cartridge, must have given it away to somebody!)

[baldie]

Star man Laurie.

Look forward to seeing you.

[onehole]

 

"This is only one example and I have seen the opposite of this occur in other calibres/rifles as well!!!!"

 

Just had a play with my 308 and checking "Jam" figures as its been a while since I last checked for any wear[around 300 rounds ago]It appears around two thou has gone since the last check,certainly no more but both heads that I use , 155 AMax and 155 scenar showed the same movement.More interesting is a comparison of figures using the "modified standard case" and my once fired fitted case to take these measurements.The "Jam" OG for the modified case was 2.234 and for the once fired and fitted case 2.230, only 4 thou but different all the same and a "reverse" trend compared to my 6br where the once fired and fitted case gave the longer OG figure.I load to 2.215 so not a problem even if the error was not known to me but in any event I would suggest anyone that plays "close to lands" or "think they are" should take a closer look at any markings on an extracted dummy/live round just to see if there are any land engravings you were or were not expecting!!! Take care Onehole.