Thread: Gordon's Reloading Tool - barrel length question

Hi All, Couple of quick questions on using GRT.

How should barrel length be measured for input into GRT? Found a thread that says it should be the distance from bolt face to the crown. That would mean I have a 26in barrel when i thought I had a brand new 22in barrel. Obviously there's a huge difference in GRT output between 22in and 26in so need to get that right.

Also trying to make GRT output fit (as much as possible) some measured velocities on a new load, by adjusting 'initial pressure' and it gets very close is when 'initial pressure' is set to zero. Instructions say that 'initial pressure' is there to be used as an adjustment for this purpose - is setting this value to zero reasonable as long as it calibrates GRT with real world velocity results?

Any advice appreciated, cheers.

No way is there a 4 inch difference. You aren't measuring with the bolt open are you?

Use the OBT tool to auto-adjust the powder to match real-world results. You can change initial pressure beforehand, but keep it realistic.

Originally Posted by Pommy

No way is there a 4 inch difference. You aren't measuring with the bolt open are you?

Use the OBT tool to auto-adjust the powder to match real-world results. You can change initial pressure beforehand, but keep it realistic.

No, bolt closed but just realised I stupidly read my measuring tape wrong by 100mm - so problem solved .

Ok will use the OBT, had played around with that but was hoping there was a way to adjust a string of powder weights at once rather than one at a time.

Seems a bloody good tool for calculating safe max powder weights, especially as its free.

Cheers Pommy

GRT is a fantastic tool. Lots to be learned from it, but remember it's only as good as the quality of the inputs.

Don't use it as a way to short-cut the start low and work up mantra. And always double check the inputs - case capacity needs to be measured by you in your brass as it makes quite a difference to the outputs. Also don't assume any defaults are correct (other than powder) as I found a projectile length from the library that was quite wrong that could have put me a fair way overpressure!

Originally Posted by Steelisreal

GRT is a fantastic tool. Lots to be learned from it, but remember it's only as good as the quality of the inputs.

Don't use it as a way to short-cut the start low and work up mantra. And always double check the inputs - case capacity needs to be measured by you in your brass as it makes quite a difference to the outputs. Also don't assume any defaults are correct (other than powder) as I found a projectile length from the library that was quite wrong that could have put me a fair way overpressure!

Good points. Yes I plan on using it as an interesting supplement to the traditional method of working up a load. Have measured all inputs and will look with interest at whether the outputs come close to measured results.

I recently re-barrelled to 6.5x47L and have heard/read/found that the usual pressure signs in this calibre are difficult to detect, as it's designed to take high pressures. I don't want to push it to sticky bolt stage so am being pretty conservative despite seeing a heap of guys using what look like pretty hot loads online ('murca mostly). Have only tried working up a load for 143 gr ELD-X and found a nice broad accuracy node around 34.5gr AR2208. Retro-fitting the data from this testing into the OBT function in GRT came out with predicted node of exactly 34.5gr, which I was pleasantly surprised at. It also confirmed that this and all the other powder weights tested, which I'd used ADI's powder guide to set, were well under Pmax pressure. So it's a useful way of supplementing other data sources at this stage.

Sounds like you're on the right track then. What results have you got with the 6.5 Lapua so far? It's a sweet wee cartridge.

Some of the stuff you see on the US forums seems optimistic at best, outright dangerous at worst!

Worked on Gordons this morning for the first time in quite a while and were shocked to learn that Gordon passed away on 19 January. May he RIP, he did us a huge favour.

Still trying to up load it!

Originally Posted by Steelisreal

Sounds like you're on the right track then. What results have you got with the 6.5 Lapua so far? It's a sweet wee cartridge.

Some of the stuff you see on the US forums seems optimistic at best, outright dangerous at worst!

Yep the more I read about it the keener I got. True Flite put a new barrel on my Sako 75 a few weeks ago, very happy, they did a great job and fantastic to deal with. Started OCW on 143 ELDX a couple of weeks ago but only done powder weight testing so far. 11 x charges between 32.4gr - 35.4gr AR2208 in 0.3gr increments @ 0.020" off the lands and there's a really clear node between 34.2, 34.5, 34.8, those 3 groups were at near identical vertical distance from POI. Even at a nominal 0.020" those powder weights put 3 shots each inside 0.55 inch, 0.42 inch and 0.71 inch at 100m so I'm looking forward to seeing if I can bring that down to a ragged hole with seating depth adjustment. So only early days but this cartridge seems to be living up to its reputation for being easy to tune a load for! Velocity for 34.5gr is only around 2600fps so a bit slower than I'd prefer but I'd rather nail accuracy and it'll still put down anything I aim at out to 400-500m max, which is about as far as i can see anyway.

Definitely agree about some loads you see on US forums, seen plenty talking about loads well above max pressure. The 6.5 Lapua seems to give you a false sense of security with its ability to handle pressure and lack of pressure signs, I'd rather be conservative and sacrifice a hundred or so fps and be sure the bolt isn't about to drill me a new nostril!

Having said that - anyone have any experience or advice on pressure signs and max powder loads working up loads in this cartridge?

Originally Posted by Jaco Goosen

Worked on Gordons this morning for the first time in quite a while and were shocked to learn that Gordon passed away on 19 January. May he RIP, he did us a huge favour.

Yeah saw that as i was downloading the programme, sad news. Pretty amazing legacy he leaves behind though, I wonder how many people have avoided serious injury through his work?

I for the life of me can’t figure it out painful computers are not for me