7.5 x 55 Swiss - Quickload Request

R

RC20

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This is the first time I have made a request, not something I need normally.

I am shooting a modern 7.5 Swiss barrel on a modern action (I built it up, aka its a Savage receiver)

I ran into a pressure limit with R17 and 7.5 with 175 grain Sierra Match bullet.

I hit 51.5 grs and got a definite hard to lift bolt. Primer ok, little flattening but I am not one to need more than a harder bolt lift to back off.

I would like to know what kind of pressures Quckload shows for that?

As the 7.5 Swiss is a 30-06 capacity case, the dynamics seem to be very different as the load is not close to 30-06 maximum (54.5 per Alliant for a 180 gr) )

I pulled all the rest down and backed it down a half a grain as previous load was ok there.
 
CAUTION: The following post includes load data generated by calculation in QuickLOAD software based on a particular powder lot, the assumption the primer is as mild as possible, and assumptions about component, chamber and gun geometry that may not correspond well to what you have. Such data should be approached by working up from published starting loads. USE THIS DATA AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL, nor QuickLOAD's author nor its distributor assume any liability for any damage or injury resulting from use of this information or information derived from it.

This may not help, but here is some data:

I load 175 SMK for a K-31, CCI 200, 48.5 Re-17, COL 2.933. That's good for 2,570/7.7 Std. GP11 go 2,579/12.3 Std. QL closely predicts my velocity (2,550) at a predicted pressure of 37,456. Since I matched GP11, I was happy and didn't go further.

At my COL, 51.5 Re-17 would yield 44,655 psi.

A couple thoughts. My COL is about as long as I can go with MatchKings. Their profile does not allow the length of the needle-nosed GP11s, at least in my rifle. Your custom chamber may be tighter than the K-31's. I put a short chambered 6.5x55 barrel on an old Mauser and finish reamed it to min spec. Some loads that do fine in my Classic Featherweight M70 are too hot in the Mauser.

This illustrates why QL, while a great tool, must be used with great caution. Good luck and good shooting.
 
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Thank you.

Virtually no data out there on a modern gun and 7.5 Swiss load.

I am working from down low quite a ways. This one was a pretty sudden cam over in regards to serious bolt lift (interesting the primer was pretty good and no smear on the case head)

The thought was that a modern gun should be able to take a 30-06 pressure.

Not sure whats at play if the shorter and fatter case really is a lot more efficient or?

It won't change my approach (start at K31 load levels and work up) but it has my curiosity tweaked.

I will do a test run of H4350 and see how that goes.
 
I did some cross checking and found the R17 in the Hornady X for 30-06

Interesting as they list a max of 48.4 for a 178 to 180 gr bullets.

That is significantly less than Alliant list for a 180 gr bullet.

At issue is Hornday is the only one that has published any R17 data other than Alliant.

Obviously its another case of cross check when you can and then go conservative.

In this case 1.6 grs more looks to be max for the 7.5/30-06 and that is born out by the end results.

Most interesting.

Seems to add relevancy that with caution you can probe up to top of 30-06 loads for the 7.5 Swiss in modern rifle.
 
QuickLOAD's listed case water overflow capacity is about 3 grains less than .30-06, so it's not surprising it doesn't like quite as much powder.

Weigh one of your fired cases and then fill it level to the mouth (no meniscus) with water and weigh it again and record the weight difference. A lot of .30-06 out of production chambers seems to come out in the range of 69-71 grains of water capacity by that method, to give you a comparison to make.
 
I'll have to see if I can find my notes.

I took a bit different tack and filled with W748 ball, smoothed off.

I think it came out the 3 gr difference you are talking about, had forgotten that. Most literature says the same so worth a check again.


Just occurred to me I should do PPU to PPU form some similarity, I do have 30-06 in that as well as PPU being the only source for 7.5.

Plenty good with that, it seems to be about RP class (at least older cartridges) and have been quite happy with RP.

Going over the Hornaday data (X Book) almost or all the powders give better velocity than the R17.

That seems to contradict the claims that you can get better velocity out of R17 as it sustains the pressure longer.

Also of note one reason I am interested is the 7.5 experts feel that R17 is the powder used in the GP11.

Too bad the Chrony died it might be some interesting stuff to look at velocity wise across the powders in 30-06.
 
The PPU experiment sounds reasonable.

RL17 isn't in the X book for the 7.5×55 that I can find. Perhaps you are looking at .30-06 loads. In that cartridge, for all bullet weights in that manual from 150 to 200 grains (except for the 195 grain bullet which is just a statistical outlier, I suspect), RL17 produces either the fastest (the 165's and 168's on page 514) or is one of several fastest loads listed in that manual. Only with bullets outside that weight range does it drop behind, being too fast for highest velocity in the over-200 grain bullets, and two slow for it in the sub-150 grain bullets.

The reason RL17 doesn't show in the 7.5×55 data is the lower peak pressure, I expect. This powder requires adequate pressure to not to burn inefficiently, and the pressures Hornady lists for this round are intended to be safe in guns that leave a lot of the head unsupported and have to avoid pressures that might blow the case out, an event that usually destroys the magazine and splinters the stock. Your gun is not in that situation, though, so you should be able to run it higher.

I'm thinking there might be another chronograph in your future, so you can prove it to yourself.
 
I don't shoot 7.5x55 any more but when i was loading a lot, 10-15 years ago, when they first hit the US market, I was sticking pretty close to .308 loads. I liked 4064 and 168 SMK's, for what it is worth.
 
You should have cut your load by a grain to two grains. I am confident you were over max before you got sticky extraction.

I loaded WC852 and AA4350 in my K31 and I kept my velocities close to Swiss ball. Never tried the powder you are using.
 
The 7.5 Swiss experts are adamant that R17 is the powder used for the GP11 rounds in a K31(and safe in that gun) at around 50 grains.


In this case I am shooting a modern receiver with a push feed bolt (supported) with a 7.5 Swiss Chambered barrel so we are not talking K31 here (and I sure would be back off 2 grains for that gun)

I was a bit surprised Hornady did not list it in the 7.5 choices as the 7.5 Swiss board is adamant that is the powder used in the GP11 (K31 fodder as it were).

The 7.5 Swiss group has it pegged at around 50 grains for the 174 GP11 bullet.

That said, I have some serious egg on my face.

I went back and checked the 30-06 load levels. I had looked at 308 instead of 06.

Bit of a Surprise as Horandy 9 lists the 178-180 grin at 52.1 and 2650

Hornady 10 lists it at 55.7 and 2750 (equals 3 other new powders including Superpeformance)

Head scratcher as to why same capacity case in a modern gun won't take over 50.

As for backing off, previous was 1/2 grain lower. It looked like it was getting into a good node and I thought I had some up side to go.

I don't normally shoot full loads, but if it is a good one I will. This was looking really good and wanted to see how wide it was.
 
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