Throat errosion

[GSP7]

I have a 6.5x55 m70 I have about 400 rds through it and use r22.

After cleaning, examining the throat,thought I had carbon at the throat)Looks like I have some throat errosion.

Measured my different bullets in a dummy case again and compared to my old data and looks like im about .010-.020+ longer c.o.l. to lands.

Only 400 rds. Hmmm... Am I not letting the barrel cool enough??

Tell me about errosion, prevention, dealing with it etc.

Isnt R22 double base? Could useing H4831,h4350 help? Isnt H4831, h4350 single base? Doesnt double base powders eat throats faster?

Thanks Rick

 

[BoydAllen]

I heard, from an excellent source, based on actual experience of a number of shooters, that the Reloader powders are more erosive than their "H" equivalents. In many applications this may not matter too much, but these were highpower shooters that put a lot of rounds through their long range bolt rifles per year.

My loading for the 6.5 x 55 has primarily been with IMR 4350 for light bullets and the old,pre-Extreme)H4831 for heavier bullets. I never got much accuracy with the medium weight bullets, but got excellent accuracy with 100 grain Sierras,4350) and also with 160 gr. Hornadys,4831) In Swedish Mausers with open sights I have grouped five under 3/4" and three well under that with the 100s, and three under 3/4 with the 160s. This may not seem all that great, but one needs to remember that these were unmodified military rifles with open sights. If you put a set of those sights on my benchrest rifle, I doubt that I could do better.

A friend who had the same rifle that you have, worked up an accurate load with 129gr. Hornadys and IMR 4831.

 

[GSP7]

I just tryed H4831/140 sierra and got a 1" 5 shot group at 100 last weekend. 4 of the rds were 3/4".

I was cleaning up the bore to play with some H4350 next.

The old speer book says the H 4831 and 4350 are single base. I know Hodgdon calls them extreme powders now, are they still single base?

 

[Forum Boss]

What is your barrel cleaning procedure? How often do you brush and do you use any abrasives?

Regarding the barrel-eroding effects of double base powders such as N540 and N550, I have no doubt that there may be empirical evidence of this in some rifles, but one thing to keep in mind is that, oftentimes, shooters choose these powders to achieve the absolute maximum velocities with a given bullet/cartridge combo. With the 6.5x47, for example, in testing loads with the 139gr Scenar, there's no question that N550 is yielding more velocity than most of the suitable single-base options, at least with the 139s.

So are double base powders bad? In fairness I think you have to look at what happens at the same velocities. If you load the double-base down to a velocity that is the equivalent of what you might get with a single-base powder, I'm not convinced the increased throat erosion is as great as some people think. The point is, yes, maybe you're giving up some barrel life but the double base may get you to an important accuracy node and that may be more important. One has to look at all the pros and cons.

 

[BoydAllen]

The shooters that I wrote about were not trying to wring the most velocity out of a small case, and I was only talking the slower end of the Reloader powders. Specifically, the fellow that I was speaking is a High Master who is,and was) well acquainted with the best in highpower that our state has to offer. This may have been more than ten years ago that I spoke with him about this subject. Also, I believe that it is possible to modify powders to reduce erosion. If you read down a ways, you will see that in the case of the VV 500 series, this has been done. I am not sure that this is the case with RL22, for instance. It may be that all double base powders are not the same with regard to erosive potential.

N500 series
Adding nitroglycerol to the traditional single base powder
makes possible in addition to geometry and coating
a third controlled variable of ballistic properties: energy
content. Vihtavuori calls powders which have nitroglycerol
added,maximum 25 %) high energy NC-powders,
which form N500 series.
Adding nitroglycerol to the high energy N500 series is
done by impregnation. After that the grains are coated
with a new type of chemical which results in very
progressive burning characteristics.
The composition of a typical high energy powder is as
follows:
* nitrocellulose * nitroglycerol
* coating agent * stabilizer
* flame reducing agent * wear reducing agent
Geometrically the powders in the N500 series are equal
to the N100 series. Although these new powders have a
higher energy content, they do not cause greater wear to
the gun. This is because the surface of the powder has
been treated with an agent designed to reduce barrel wear.
N500 series powders work well at different temperatures,
even better than the traditional N100 and N300 series.
Temperature sensitivity naturally depends very much on
the weapon and on the cartridge. The manufacturing
technique employed permits a very high bulk density,
which in turn makes it possible to use a bigger charge in
a certain limited loading volume.
Vihtavuori High Energy powders are available in for
burning rates:
N530: Burning rate close to N135. Especially for .223
Remington. Excellent also for .45-70 Government.
N540: Burning rate like N140. Especially for .308 Winchester.
N550: Burning rate like N150. Especially for .308 Winchester
and .30-06 Springfield.
N560: Burning rate like N160. Especially for .270 Winchester
and 6.5 x 55 Swedish Mauser.

 

[Lane]

I have a 6.5x55 m70 I have about 400 rds through it and use r22.

After cleaning, examining the throat,thought I had carbon at the throat)Looks like I have some throat errosion.

Measured my different bullets in a dummy case again and compared to my old data and looks like im about .010-.020+ longer c.o.l. to lands.

Only 400 rds. Hmmm... Am I not letting the barrel cool enough??

Tell me about errosion, prevention, dealing with it etc.

Isnt R22 double base? Could useing H4831,h4350 help? Isnt H4831, h4350 single base? Doesnt double base powders eat throats faster?

Thanks Rick

It is my understanding that factory chambers are cut with a reamer that starts out at the SAAMI maximum dimensions and is used until the reamer cuts a SAAMI minimum dimensioned chamber. Your particular chamber was cut at some-point in this process. Lot's of discussion about powder! Erosion will be affected by combustion gas, bullet friction and heat in my opinion. The volume of powder that can be burned up is controlled by the dimension of the case. At firing the dimensions of the case will be controlled by the chamber. Combustion gas will change the external dimensions of the case to fit the chamber. A chamber cut toward the minimum dimension,tight chamber) will in effect reduce case volume and increase chamber pressure,heat). A,loose) or chamber reamed to maximum dimensions at firing will allow for the external diminsions of the case to expand until controlled by the chamber. Loading density is greater and chamber pressure is lower. You could have a lot of disscusion about a chambers throat or lead. OAL varies from bullet to bullet and round to round. The origin of the rifling is being eroded away and this normal. Lane