Thread: 303 MK7 load data?

Originally Posted by Jhon

I tend to load mostly cast bullets in my 303B these days running under 2000fps. Getting sights sorted that are regulated for military use is an issue but my 303s are all sporterised versions..a scope sorts any sighting issues. A target ladder/aperture sight would also give you this.

Anyway, looking at ADI current data for say, 174gn, I'd personally call a "modest" charge anything in the bottom half of the listed range. For a velocity in the 2100 fps range. If you start looking for velocity around max or even above thats where I would expect to get shorter case life. Others might want to venture different views here. I've not played with lighter weight bullets in the 303B but I've read of folk using for instance, pulled 124gn 7.62x39 projectiles. I suspect you'd need a decent bore. ADI has data for a Speer 125gn bullet in the 2700-2900fps range. That's pretty crisp but probably not as hard on cases due to the lower inertia of the lighter bullet. If you used Trailboss or say an appropriate Pistol/Shotgun powder you could develop quite a low stress plinking load. I've read and saved somewhere info on folk doing this. Be aware tho that low velocity doesn't automatically mean low pressures. It's not hard to blow things up using these powders in rifle as they peak pressure very quickly. Use published data for Trailboss and for the others start at around 8gn and stay below 12.5. For subsonic work downwards from.8-10gn checking bullet leaves the barrel. Do any of this at your own risk. I use a charge of 6gn Nobel 78 Shotgun powder (equivalent to AS30N and/or Red Dot) for subsonic 189-200gn cast bullets and up to 12gn for 1600fps..Absolutely no fillers used. YMMV.

Our club is using alot of military rifles in their original configuration and sights etc, many still shooting the old CAC stuff with cordite which im now trying to avoid.
Im not sure what standard people are using for competitive sports, but I do know that many seek the standard 174 grain flat base bullets that are no longer produced.
It appears that a load of 46 grains or so is getting near the top end for 2440fps, so not exactly modest, but will be interesting to see how many reloads I get.

Originally Posted by grandpamac

The lengthening of the case is likely due to a combination of loose headspace at the rim and a roomy chamber. The stretching mostly happens a little ahead of the head and this is where it will crack if the case is FL sized repeatedly. When a .303 round is fired the case is driven forward in the chamber by a combination of the firing pin strike and the primer firing until it is stopped by the rim. Next the case body expands to fit the chamber. If the pressure is low the primer will be backed out of the case a little when extracted. If the pressure is high enough as with factory loads the front section of the case is gripping the chamber walls and stays where it is. The rear half is forced back by the pressure with the case stretching just in front of the head, eventually cracking at this point. To get decent case life pressure needs to be kept low enough to stop the stretching. A protruding primer will help in this.
GPM.

yes I get the feeling that the chambers on most 303 rifles are fairly sloppy.
My main concern is if i get them stretch too much and cause problems, do you typically have to shorten 303 cases much because of this?
Looks like 56.4mm is the maximum length, but my cases are closer to 56.5mm, if i keep the same cases for each rifle, will they stay the same length as the chamber?

First you need to understand what's going on with the .303 that is different to a rimless cartridge.

The .303 headspaces on the rim. The shoulder does not contact the chamber prior to firing. When fired, the brass expands into the chamber and the shoulder is blown forward to fill the chamber.
Compare a new, unfired case to a fired case and you will see that the shoulder has moved forward. When this happens, the case stretches, particularly about 3/8" forward of the rim.

If you full length size the case, it will stretch again when fired.

If you only neck size without touching the shoulder, then the case will head space on the shoulder for future firings. This reduces stretch and helps with accuracy. Over time, the brass does still flow forward, so you will have to trim the length, but not as much as if you are full length sizing.

If you full length size, you can expect case head separation in as few as 3 or 4 firings, whereas neck sizing can give 10 or more reloads.

In my opinion, the Lee collet die is an absolute must for the .303. I use around 46.5gr AR2209 with a 174gr projectile.

Originally Posted by Old_School

Our club is using alot of military rifles in their original configuration and sights etc, many still shooting the old CAC stuff with cordite which im now trying to avoid.
Im not sure what standard people are using for competitive sports, but I do know that many seek the standard 174 grain flat base bullets that are no longer produced.
It appears that a load of 46 grains or so is getting near the top end for 2440fps, so not exactly modest, but will be interesting to see how many reloads I get.




yes I get the feeling that the chambers on most 303 rifles are fairly sloppy.
My main concern is if i get them stretch too much and cause problems, do you typically have to shorten 303 cases much because of this?
Looks like 56.4mm is the maximum length, but my cases are closer to 56.5mm, if i keep the same cases for each rifle, will they stay the same length as the chamber?

Greetings,
After a break of some 40 years I timidly entered the .303 world again around 10 years back for an iron sight comp. I had been loading light loads for 4P shooting mostly at 100 yards in my .308 using 40 and later 38 grains of AR2206H with 150 grain projectiles. The .303 rifles bore was good but not pristine and an arbitrarily selected load of 40 grains of the older AR2209 with the 174 grain Hornady round nose. Cases were sized with a Lee loader. Previously fired cases from a different rifle chambered and were used. I found very little stretching that I could detect and even cases that chambered snug chambered freely after firing. Velocity was around 1,950 fps and accuracy good. So in answer to your question you will need to trim cases after their first firing but if you keep the same cases for each rifle and neck size preferably with a Lee loader or Lee collet die and keep pressures low little if any trimming should be needed. I would steer clear of conventional neck sizing dies as some makes tend to oversize the brass which can lead to case stretching. When the neck is sized down it becomes longer. It shortens when it is expanded but not as much. this happens with the two neck dies as well but not to the same extent.
GPM.

Originally Posted by Crusty

First you need to understand what's going on with the .303 that is different to a rimless cartridge.

The .303 headspaces on the rim. The shoulder does not contact the chamber prior to firing. When fired, the brass expands into the chamber and the shoulder is blown forward to fill the chamber.
Compare a new, unfired case to a fired case and you will see that the shoulder has moved forward. When this happens, the case stretches, particularly about 3/8" forward of the rim.

If you full length size the case, it will stretch again when fired.

If you only neck size without touching the shoulder, then the case will head space on the shoulder for future firings. This reduces stretch and helps with accuracy. Over time, the brass does still flow forward, so you will have to trim the length, but not as much as if you are full length sizing.

If you full length size, you can expect case head separation in as few as 3 or 4 firings, whereas neck sizing can give 10 or more reloads.

In my opinion, the Lee collet die is an absolute must for the .303. I use around 46.5gr AR2209 with a 174gr projectile.

Yes, thats what Ive noticed with my fired cases. From what I gather this expansion is experienced in all firearms to some degree, but with the 303 is notably greater.

Even though the 303 headspaces on the rim, it would appear that there is still quite a bit of space between the neck and chamber wall compared to other calibers.
Something else Ive learned, is what I and others considered to be headspace is actually head clearance, seems many people get these two mixed up, but i see that too much head clearance on these rifles can cause extra case stretching too.

Ive seen some say the loose space was intentional to allow dirty rounds covered with mud to still chamber in a battlefield situation, others say its just a result of them being mass produced with low tolerances, I also read that the bolt can move back a bit when fired which also allows the case to expand lengthwise.
Im not 100% sure what of any of this is true, there seems to be a ton of opinions on this on the internet, all I do know is its pretty evident that there is room for expansion in the chamber on these rifles.
I definitely want to grab one of these lee collet dies for sure.

Originally Posted by grandpamac

Greetings,
After a break of some 40 years I timidly entered the .303 world again around 10 years back for an iron sight comp. I had been loading light loads for 4P shooting mostly at 100 yards in my .308 using 40 and later 38 grains of AR2206H with 150 grain projectiles. The .303 rifles bore was good but not pristine and an arbitrarily selected load of 40 grains of the older AR2209 with the 174 grain Hornady round nose. Cases were sized with a Lee loader. Previously fired cases from a different rifle chambered and were used. I found very little stretching that I could detect and even cases that chambered snug chambered freely after firing. Velocity was around 1,950 fps and accuracy good. So in answer to your question you will need to trim cases after their first firing but if you keep the same cases for each rifle and neck size preferably with a Lee loader or Lee collet die and keep pressures low little if any trimming should be needed. I would steer clear of conventional neck sizing dies as some makes tend to oversize the brass which can lead to case stretching. When the neck is sized down it becomes longer. It shortens when it is expanded but not as much. this happens with the two neck dies as well but not to the same extent.
GPM.

Thanks, I will keep that in mind.
I was in at Reloaders supplies yesterday to get my powder but they had no Lee collet dies in stock, but I should be able to get one in.
Meanwhile, I still have enough cases to load that have not been fired yet, will need to measure all the other cases ive got to see how many need trimming.

Well here are my first reloads.
All fired successfully with modest recoil.
I aimed at the centre of a piece of plywood and got 150mm average groupings with iron sights at 50m away. Need to test groupings on my scoped rifle next time.

Anyway, no real issues to speak of.
Case appears to possibly be more stretched, neck looks slightly shorter.
Im not sure if this is just a more sloppy chamber in this rifle yet, its the first time I've fired this.
See the photo alongside a factory HXP load (tarnished case) both were individually fired in separate rifles.

Well here is an update on the chronograph readouts from various loads along with readings from HXP that ive got.
I fired 3 HXP rounds as a ballpark figure and their velocity is pretty shit, from what I understand, they are supposed to have a velocity of 2400fps, this could be due to age however and their poor storage conditions.


HXP velocity as follows x3 rounds:
2149, 2134, 2132fps

AR2209 loads as follows:
45.5gr 2321fps
46gr x2 2340fps and 2364fps
46.5gr 2368fps
47gr x2 2395fps and 2379fps
47.5gr 2455fps

Looks like somewhere close to 47.5 grains will give the desired velocity, however I would need to try several more loads to work out an average and test in different rifles.
I hope this is help to anyone else wanting to do MK7 loads with the original flat bottom projectiles.

Originally Posted by Old_School

Well here is an update on the chronograph readouts from various loads along with readings from HXP that ive got.
I fired 3 HXP rounds as a ballpark figure and their velocity is pretty shit, from what I understand, they are supposed to have a velocity of 2400fps, this could be due to age however and their poor storage conditions.


HXP velocity as follows x3 rounds:
2149, 2134, 2132fps

AR2209 loads as follows:
45.5gr 2321fps
46gr x2 2340fps and 2364fps
46.5gr 2368fps
47gr x2 2395fps and 2379fps
47.5gr 2455fps

Looks like somewhere close to 47.5 grains will give the desired velocity, however I would need to try several more loads to work out an average and test in different rifles.
I hope this is help to anyone else wanting to do MK7 loads with the original flat bottom projectiles.

good stuff. i still have some old mk7 to shoot off but i will keep this in mind when i reload 303!

Originally Posted by Russian 22.

good stuff. i still have some old mk7 to shoot off but i will keep this in mind when i reload 303!

Will be interesting to compare how you go if you can get a reading.
Im still not sure if i need to chase up the whole thing on barrel harmonics or not, but Im happy if I can get the 2400fps target.
46.4grains should do it i think.

Greetings @Old_School,
A lot of .303 barrels are pretty worn and produce velocities well short of those less used. Pressure barrels are made to tight tolerances so there can be a big gap between current published velocity and what the handloader will achieve. A few years back I subscribed to Loaddata.com and found some data that Brian Pearce had shot in a No4 Mk1 with the standard barrel. His data was for the Hornady 174 grain RN or FMJ BT and pressures were kept low with respect to the age of the rifles likely to be used. He did not load AR2209/H4350 but did load IMR4350 which is close to AR2209 these days. He gave a list of increasing loads and velocities quitting at 44.6 grains of IMR4350 for 2,227fps. Extrapolating from that 45.5 grains of IMR4350 should produce around 2,270 fps and 46.5 grains 2,330 fps. Your rifle is producing a little more velocity for whatever reason. My 40 grain load with the 175 grain RN came in a little slower as expected, 1,945 fps calculated v 1,930 fps chronographed.
To be clear I don't post load data from Loaddata.com on the internet but do use limited quotes in my posts where it helps understanding.
Regards Grandpamac.

Originally Posted by grandpamac

Greetings @Old_School,
A lot of .303 barrels are pretty worn and produce velocities well short of those less used. Pressure barrels are made to tight tolerances so there can be a big gap between current published velocity and what the handloader will achieve. A few years back I subscribed to Loaddata.com and found some data that Brian Pearce had shot in a No4 Mk1 with the standard barrel. His data was for the Hornady 174 grain RN or FMJ BT and pressures were kept low with respect to the age of the rifles likely to be used. He did not load AR2209/H4350 but did load IMR4350 which is close to AR2209 these days. He gave a list of increasing loads and velocities quitting at 44.6 grains of IMR4350 for 2,227fps. Extrapolating from that 45.5 grains of IMR4350 should produce around 2,270 fps and 46.5 grains 2,330 fps. Your rifle is producing a little more velocity for whatever reason. My 40 grain load with the 175 grain RN came in a little slower as expected, 1,945 fps calculated v 1,930 fps chronographed.
To be clear I don't post load data from Loaddata.com on the internet but do use limited quotes in my posts where it helps understanding.
Regards Grandpamac.

Yes I wondered if that could be the case here, the rifle i did these tests on appears to have a good barrel, but I have not slugged this bore or put a bore gauge in it yet, but when i place a round in the muzzle it does not drop down far.
I do have another rifle which I do know has a very tight bore when measured, so would have been good to make a comparison in that rifle too.
I also believe that even from new, tolerances in the barrels was poor with some being looser than others, I believe this was a major issue with some no4 rifles having very sloppy barrels from what ive been reading.
If i find that the velocity is higher in my other rifle, I will tweak down the load, its probably a good idea to average it over several rifles to work out how it performs.
The fella with the chronograph said that he measured some old cordite loads in his rifle and they all were spot on around the 2400fps mark that they are supposed to be, but I dont know the condition of his barrel.